Talk:Alpha Centauri/Archive 2

Confusion
Seems this paragraph confuses the two stars:

''Conversely, some similar Earth-like planet at 0.71 A.U. from α Cen B would receive significant illumination from α Cen A, which would shine 4.65 to 7.3 magnitudes dimmer than the Sun at visual magnitudes of −22.1 to −19.4, respectively. Similarly, α Cen B would be 70 to 840 times dimmer or some 520 to 6300 times brighter than the full moon.''

How on a planet on an orbit at 0.71 A.U. about Alpha Centauri B, Alpha Centauri B can be seen 840 times dimmer than the Moon?--MathFacts (talk) 03:17, 26 February 2010 (UTC)
 * Perhaps the sentence is just written badly? I think it means this: Similarly, α Cen B would be 70 to 840 times dimmer [than the Sun] or some 520 to 6300 times brighter than the full moon. HumphreyW (talk) 07:42, 26 February 2010 (UTC)
 * At 0.71 AU from α Cen B it cannot be 840 times dimmer than Sun at Earth because it is just the distance at which it should look just as Sun looks on Earth. α Cen B naturally 2 times dimmer than Sun at the same distance. So when closer to α Cen B than 1 AU it even theoretically cannot be dimmer more than 2 times than Sun, not to say 840 times.--MathFacts (talk) 01:13, 27 February 2010 (UTC)

Good point guys. I agree, it is a mess. I have simplified and clarified the offending text so it makes more sense. Note that the issue that makes it more complicated is that the luminosity of the stars is different, hence, different distances (in AU) from the hypothetical planets. The selected distances as referenced in Crowell are based on the necessary habitable zones of alpha centauri. Also the orbital of alpha centauri is far more elliptical than any of thee planets, and it is this distance that causes the brightness variations. The brightness are based on the companion, which varies between about 11.9 AU (Earth to Jupiter) and 34.9 AU (Earth to Neptune). So while the orbiting star of the planet is −26-odd magnitude, at 11.9 or 34.9 this brightness will be quite different (dimmer). This is values used for the magnitudes calculated. The values in the text are the visual magnitudes at these distance. The relative magnitude ratio (MR) is calculated from the difference in magnitude, using MR =2.512^x, where x is the difference in magnitude or delta-m. I.e 2.512^4.5=870 times difference in brightness at −22.1 magnitude object from Alpha Centauri B. (Similarly, at farthest, this is 2.512^7.3= at −19.4 or 2700 times dimmer, etc.)

I notice too that some off his values here are slightly different.

Alpha Cen A (from Planet around B) should be (if Sun is −26.8)

Min Dist:

Mag = −22.1

Δm = 4.7

BrightRatio =  76

Max Dist

Mag = −19.4

Δm = 7.4

BrightRatio = 910

Alpha Cen B (from Planet around A) should be (if Sun is −26.8)

Min Dist:

Mag. = −21.0

Δm = 5.8

BrightRatio = 208

Max Dist

Mag = −18.2

Δm = 8.6

BrightRatio = 2800

Alpha Cen A (from Planet around B Comparison with moon (if Moon is −12.6)

Min Dist

Mag = −22.1

Δm = 9.5

BrightRatio =  6300

Max Dist

Mag = −19.4

Δm = 6.8

BrightRatio =   520

Alpha Cen B (from Planet around A Comparison with moon (if Moon is −12.6)

Min Dist

Mag =  −21.0

Δm = 8.4

BrightRatio = 2300

Max Dist

Mag = −18.2

Δm = 5.6

BrightRatio = 173 If more precision was required, then the real difference between best opposition (orbiting Alpha Cen A, look at B) when closest is at;

11.9-(1.34/2) AU or 11.23 AU

and at furthest distance opposition

34.9-(1.34/2)= 32.4AU,

or if at superior conjunction at

34.9+(1.34/2)= 35.6 AU.

From Alpha Cen B, these values are;

11.9-(0.71/2)= 11.54 AU,

34.5AU, and

34.9AU, respectively

This kind of accuracy is not required, but explains the logic here!!

Magnitudes (mv) quoted here are from the absolute magnitude (Mv) corresponding to the distance (d) instead of 10pc. reduced to distances as quoted (AU converted to parsecs.)

I.e. mv= Mv + 5(log10 d-1)

1 parsec= 206265 AU

If Mv (A) = 4.38 and Mv (B) =5.71

Then at; 11.23AU ;

Max Apparent Magnitude for A

= 4.38 +5 × (log10 11.23/206265 −1)

= -21.94 or −21.9

32.4AU ;  Min Apparent Magnitude for A

= 4.38 +5 × (log10 32.4/206265 −1)

= -19.63 or −19.6

Then at; 11.23AU ; Max Apparent Magnitude for A

= 5.74 +5 × (log10 11.23/206265 −1)

= -20.58 or −20.6

32.4AU ; Min Apparent Magnitude for A

= 5.74 +5 × (log10 32.4/206265 −1)

= -18.28 or −18.3

Sun at 1.00 AU with an Mv of 4.8, the magnitude is -26.7 (as used above.) (-26.8 with Bolometric Correction)

All these values are close to the article itself.

Hope this all helps.

Arianewiki1 (talk) 01:40, 10 May 2010 (UTC)

Updated values
The following 2008 reference:

contains updated parameters that differ somewhat from the values in this article's infobox.&mdash;RJH (talk) 14:36, 8 May 2010 (UTC)

Question
Does anybody know if Alpha Centauri can be resolved into a binary star system with field binoculars, rather than a telescope? Thanks. HowardMorland (talk) 16:37, 20 May 2010 (UTC)

Why is this?
"In addition, the lack of any brown dwarfs or gas giants around A and B make the likelihood of terrestrial planets greater than otherwise." —Preceding unsigned comment added by 138.251.236.141 (talk) 11:50, 26 June 2010 (UTC)


 * Since this appears to be a point of confusion for at least one person I have moved the cite up and duplicated is below to show that both sentences are covered by the same reference. HumphreyW (talk) 12:35, 26 June 2010 (UTC)

Spatial orientation of the orbit: Ascending or descending node
Does the longitude of the node refer to the ascending or descending node (here I mean with "ascending" that the secondary star is moving towards the observer when it passes it; I don't know whether this is the correct definition because the article Longitude of the node does not give any useful answer to this question)? Since Alpha Centauri is the closest binary system the radial motion of its components should be well known and thus the orbit be known unambiguously. Unfortunataly, Google does not seem to be able to present anything here then either Wikipedia articles or completely unrelated stuff.--SiriusB (talk) 22:51, 27 June 2010 (UTC)

Update: According to Pourbaix et al. (2002, the reference for orbital elements in the Article Alpha Centauri, see ) the relative radial velocity of A vs. B became zero (i.e. both had the same RV wrt. the Sun) in 1927 (interpolation of the time marks in subfigure of Fig. 2), and so in 2007 one orbital period later. B's RV curve is that with the larger amplitude (open symbols) due to its lower mass, and it switched from larger to smaller than A's RV in 2007, so it reached its maximum radial separation from A behing behind A. In other words, α Cen A is currently the second nearest neighbour to the Sun after Proxima. Maybe one could create another orbital plot with the following improvements: 1. Color (or other) coding of the near/far position of B vs. A, 2. timestep set to 1 year (or, as a good approximation, 1/80 of the orbital period), 3. labels for periapsis and apoapsis position with years (next periapsis will be in May/June 2035). I would do it myself, but however, do not have the appropriate tools to create these nice shiny sun-like points in the figure. Note that the times refer to the arrival of the light at the Earth. The true times are 4.365 years ealier (neglecting any special or general relativistic corrections). As a first step, I have mentioned the far position of B in 2007 in the (now rather full) caption.--SiriusB (talk) 09:41, 29 June 2010 (UTC)

Update.1: I've just installed Celestia 1.6 and found that the orientation of A vs B seems to be wrong there. At first sight I would simply assume a sign error in the near-far orientation problem mentioned above. Indeed, it had been very hard to me to find out the real orientation, and RV vs. time plot shown in Pourbaix et al. (2002, and cited sources in that paper) was the first direct hint that B is indeed currently "behind" A. I suppose that refereed papers are more reliable than Celestia here.--SiriusB (talk) 08:32, 2 July 2010 (UTC)

Update.2: I do confirm that, in the orbital solution I published in 2002, the longitude of the node refers to the B component and it is indeed the ascending node (no ambiguity in a visual double-lined spectroscopic system). --Dimpbx (talk) 07:00, 26 July 2010 (UTC)

Total Magnitude of Alpha Centauri
There seems to be some confusion about the brightness of Alpha Centauri, which needs to be cleared up. Alpha Centauri comprises two stars of (A and B) being -0.01 and +1.33 magnitude. As these stars are not resolvable to the naked eye, the magnitudes are combined, making the total magnitude of the star. Alpha Centauri to the naked-eye is a single star.

To calculate total magnitude; MagA=-0.01; Flux=10^(-0.4*-0.01) = 0.9908 MagB=+1.33; Flux=10^(-0.4*1.33) = 0.2938 Add fluxes together, 0.9908+0.2938=1.2845 Take log10 of total flux, log (1.2846)=+0.11 Total Magnitude [log (flux)] = +0.11/-0.4 = −0.27  Therefore the TOTAL magnitude of Alpha Centauri as a SINGLE STAR TO THE NAKED-EYE is -0.27 (As the text already states, twice!)

Compared to Arcturus, −0.27 is BRIGHTER than −0.04 (magnitudes are reversed), so Alpha Centauri is the third brightest star to the naked-eye, behind Sirius (-1.4) and Canopus (-0.86).

When compared as separate stars, Alpha Centauri A is FAINTER than Arcturus by 0.03 magnitudes, hence Alpha Centauri A is fourth brightest as an INDIVIDUAL star!!

As we only see a single star, Alpha Centauri to the naked eye is third brightest!

Note: The Arcturus article says −0.05. It is actually −0.04 (Says so in the databox) Changed after this edit talk!!

Arianewiki1 (talk) 03:25, 26 December 2010 (UTC)

Planetary Information is Out of Date
There is a strong indication (not proof but a strong scientific indication) of a larger (possibly gas giant) planet orbiting Proxima Centauri. This preliminary evidence has been independently confirmed by a few different observatories. Although not yet definitive there is enough cite-able evidence to mention it in the article as "strong scientific indications".

Also (in the other direction) any planet of 3 Earth-masses or larger has been ruled out for Alpha Centauri A and also B. Although this does not mean that a smaller Earth-like planet has been ruled out. Anyway, citations for all of this are out there and the article would benefit from being updated.

Telemachus.forward (talk) 04:15, 10 January 2011 (UTC)


 * If you have citations, please give them and don't just talk about them. (I'm not aware of any.) You can also edit the article yourself in this case. --Roentgenium111 (talk) 14:41, 8 June 2011 (UTC)


 * The last thing I know (from Google) is that since about beginning of 2010 Debra Fischer's team is looking for planets with a dedicated telescope (see the reference given in the article), but there are no publications yet ruling out super earths. Inofficially they may even be able to rule out Neptune-sized planets, but this is just from speaking with one German expert on this, not a publication. According to the cited paper the team expects more definitive answers after three years of study, i.e. 2013. However, if they could find or rule-out Earth-sized planets then they will probably do with at least 3 sigma (99.7%) confidence since anything less than that is typically considered evidence rather than proof. But again (@Telemachus): If you have sources that already rule out >3 Earth mass planets, please let us know. Half a year since your post should be long enough to retrieve any reliable source. Additional note: Are you sure not to mean Proxima Centauri? There has indeed been a paper by Endl & Küster (2008) ruling out 2-3 Earth mass planets in the habitable zone (see that WP aricle). But Proxima is a red dwarf with a HZ of about 0.02 to 0.05 AU, which makes a Doppler test much easier.--SiriusB (talk) 12:17, 28 July 2011 (UTC)


 * Since the apparent separation of the two stars is decreasing, due to peak in Sept 2016, chances of detecting planets is also decreasing, at least until we get more and better eyes in the sky, and this should happen when the two stars begin to separate again. Kortoso (talk) 20:55, 8 June 2015 (UTC)

conditionnal for sky appearance?
I'm not sure the conditionnal is necessary when talking about how the sky looks like near alpha centauri.

I understand we have to use it when talking explicitly about an hypothetical space traveler, but if we don't, we can just say near proxima centauri, the sky looks like...

Now, I know this is a falling tree enigma, but still:  Alpha centauri is not a fairy tale. This place DOES exist, and there IS a sky there. Whether or not there is someone to contemplate it is not the question.

--Grondilu (talk) 15:07, 23 February 2011 (UTC)

Sure. If you can't find a more elegant way to phrase that section, please go ahead. Ashmoo (talk) 15:39, 23 February 2011 (UTC)

As the author who introduced this section, the information given explains the nature of the two stars in this binary system. Whilst such planets are indeed theoretical, we have to select at least a starting point. I.e. A planet similar to Earth at similar distance from the Sun. From the many frequent questions from students to amateur astronomers that are curious about the orbit and nature of the stars — especially, when compared to the sun, IMO this text is worthwhile for the sake of clarity and unnecessary debate. --Arianewiki1 (talk) 02:34, 1 March 2011 (UTC)

Detectability of terrestrial planets within three years
The paper by Guedes et al. (2008) predicts that terrestrial planets could be detected around Alpha Cen B within only three years. Now we have 2011. If the proposed study has already started (I have heard rumours about that it has already been funded and is running, but does anyone know a reliable source for that? Which telescope is actually being used, if so?), we could probably expect interesting news within the near future. I did not find anything on the abstract service so far, and negative results are less likely to be spread in the mass media than positive ones. So maybe I just overlooked some results of planets already being ruled out down to a certain mass level (Neptune-size, Super-Earths?). However, we can probably look forward to highly interesting results (even a negative one would be interesting from the scientific point of view) within the next couple of years.--SiriusB (talk) 10:25, 16 April 2011 (UTC)


 * You might be interested in this 2009 article by Gregory Laughlin. He states that any planet above 5 Earth masses would have been discovered by autumn 2010. Since any such discovery would certainly have made big news, we can be fairly certain that no such planets exist. So Alpha Centauri has no Neptune-sized planets, while smaller super-Earths can't be excluded yet... --Roentgenium111 (talk) 21:48, 14 June 2011 (UTC)


 * Thanks for that link. However, they are focusing on alpha Cen B alone (if I'm not too mistaken), and due to its lower luminosity (hence closer HZ) and mass it would be easier to detect planets there. Personally, I think that Debra Fischer's team will have the largest chance to detect any planet there, since they have a dedicated telescope (1.5 m) for this project. We could even know right now if SIM wouldn't have been canceled...--SiriusB (talk) 13:19, 28 July 2011 (UTC)


 * "Update": Debra Fischer was supposed to give a talk on her Alpha Centauri progress in May, but it was cancelled for an unknown reason. And HARPS has announced a paper on their Alpha Centauri B planet research in a present paper on their results on other stars (, p.4). So we should soon know more about the possibility of planets around Alpha Centauri... --Roentgenium111 (talk) 13:04, 10 October 2011 (UTC)


 * I'm hearing rumors of a ~1 Earth-mass (/ sin i) planet that was very recently discovered about Cen B and published in Nature. Just a heads-up. 128.84.124.49 (talk) 16:35, 16 October 2012 (UTC)


 * "Unfortunately, stray light from α Centauri A is decreasing the quality of their data as the apparent separation of α Centauri A and B closes to a near-term minimum of 4 arc sec in December 2015. Data collected by HARPS and other teams are all similarly affected and it has been generally assumed that astronomers will need to wait a few years for the stars’ separation to increase before confirming α Centauri Bb."
 * The James Webb Telescope will launch in 2018, so that should be a good time to expect better answers. Kortoso (talk) 18:53, 31 October 2014 (UTC)

lead
I have expanded the lead to include most essential points from the article. There seem to be some minor disagreements over proper grammar in the latest edits. I note that a perfectly grammatical edit by me was reversed, described as lacking a subject, when the sentence did indeed have a subject if the reader did not pause at a comma as if it were a period. The word smaller distance is indeed better than closer or nearer. The other changes of wording are worse than the original in readability. I suggest arguing for any changes here before making them. μηδείς (talk) 01:34, 17 April 2011 (UTC)


 * You're quite right that at first I failed to notice your change to a comma, and I apologise for missing that. But I am willing to defend my other changes: for example, moving up the link to 'Sun' and the capitalisation thereof. Rothorpe (talk) 01:47, 17 April 2011 (UTC)


 * I have no problem with your choice of capitalisation and linking for the word Sun. μηδείς (talk) 01:53, 17 April 2011 (UTC)


 * Good. The other thing is the change away from 'close': I did that because we already have 'closer binary' referring to AB Alpha Centauri, and I thought it clearer to use a different adjective when moving on to Proxima being the closest, ahem nearest, to the Sun. Rothorpe (talk) 01:59, 17 April 2011 (UTC)


 * Also, you say: 'The word smaller distance is indeed better than closer or nearer.' But 'closer distance' and 'nearer distance' are quite incorrect: the difference was between 'smaller' and 'shorter', and 'shorter', I think, is more idiomatic. Rothorpe (talk) 02:04, 17 April 2011 (UTC)


 * Either smaller or, better, lesser is acceptable. Neither short nor close nor near really applies. μηδείς (talk) 02:50, 17 April 2011 (UTC)


 * I disagree: 'shorter distance' is best; but 'smaller' is acceptable, and I can't be bothered to argue any more. Rothorpe (talk) 13:48, 17 April 2011 (UTC)

New Orbit Graph
I have replaced the orbit graph with a new one that also shows the periastron/apoastron and the nodes, clarifying the spatial orientation of the orbit. Please do not interpret this replacement as any kind of offense against the original author since the reason was merely missing information. If someone finds a way to generate an SVG version it would be perfect (gnuplot fails somehow to make a non-white background in an SVG)..SiriusB (talk) 20:31, 8 August 2011 (UTC)

Shortening of orbital period
"Also the orbital period of Alpha Centauri AB is slightly shorter by some 0.006 years per century, caused by the reduced time required for the light to travel to Earth as the distance reduces."

How is that possible? If Alpha Centauri is heading towards us at a constant pace, shouldn't period be affected by Doppler effect, in which case we'd observe *shorter* but not *shortening* period as the above sentence seems to indicate. I don't have the access to the cited source. Almathea (talk) 11:32, 24 November 2011 (UTC)


 * I guess that this is a bit mis-phrased. What it means is that the offset between the "true" and the observed orbit changes by about 0.006 years per century. The offset is about 4.4 years (corresponding to the distance in light years), and the decreasing distance also reduces this offset slowly. The length of the period, however, does not change. Or, more precisely, it will eventually change due to the change of the aCen's position on its path. At the nearest point, the radial velocity will vanish and so will the Doppler shift (except for a tiny transverse Doppler shift).--SiriusB (talk) 07:33, 20 May 2012 (UTC)


 * I changed it.--Patrick (talk) 09:17, 20 May 2012 (UTC)

Rating
Okay, so if this article is in a "superlative" state by now, perhaps somebody should take it through for WP:PR and try to get WP:GA status? A B-rating, while not the worst, is pretty mediocre. Thanks. Regards, RJH (talk) 16:38, 8 August 2012 (UTC)


 * Might be best to open up discussion down below in a new section and get consensus for what needs doing. Casliber (talk · contribs) 00:58, 10 September 2012 (UTC)

Separate names
Apart from people who mistake "Rigel Kent" for a compound, is there any tradition of using "Rigel" for α Cent A, and "Kent" for α Cent B, or vice versa? It would seem to be a handy shortcut, like "Proxima" for C. — kwami (talk) 07:14, 9 September 2012 (UTC)
 * I've never heard of that. A good fix if it were but sadly we can't make new rules....Casliber (talk · contribs) 20:13, 9 September 2012 (UTC)
 * I've seen it on astronomy blogs, but AFAICT not by the professionals, so what I've seen fails NOTABILITY. — kwami (talk) 20:18, 9 September 2012 (UTC)

While we're on proper names....I'll query this sentence "This is sometimes further abbreviated to Rigel, though that is ambiguous with Beta Orionis." -I don't recall seeing this star abbreviated to Rigel/Rigil without the Kent anywhere. Did this ever happen hsitorically and can we get a reference for it at all? Casliber (talk · contribs) 01:01, 10 September 2012 (UTC)


 * Allen: "Our Century Dictionary retains Rigel, though this is better known for the bright star in Orion." That may seem obscure, but I've seen it not infrequently. Certainly more than Toliman. — kwami (talk) 06:37, 10 September 2012 (UTC)
 * Allen was written in 1899. I don't recall seeing Rigel (without Kent) anywhere. If there are old texts then that is fine, might be worth saying it's archaic, but then most alternative proper names probably are...Casliber (talk · contribs) 21:45, 11 September 2012 (UTC)

Planet discovered
Just a heads-up: probably tomorrow, announcement of a earth-sized planet in a 3.4 day orbit around alpha Cen B. Imagining this article will get a bit of attention. 132.181.42.71 (talk) 21:18, 16 October 2012 (UTC)


 * I've added a short note on this news. The story was embargoed until tomorrow, but somebody leaked the story early and Nature released the embargo today (a day early). --Theropod-X (talk) 22:07, 16 October 2012 (UTC)
 * Nothing much to say but....Wow! Bring tomorrow on!! Casliber (talk · contribs) 23:17, 16 October 2012 (UTC)

Planet Confirmed ?? or not ?? False Detection probability please
Some websites appear to state that Alpha Centauri Bb is confirmed and some state that it is awaiting confirmation. With this in mind, i would like to know the false detection probability of this planet. --EvenGreenerFish (talk) 09:25, 17 October 2012 (UTC)
 * Agree - it should become clearer over the next few days. Casliber (talk · contribs) 11:20, 17 October 2012 (UTC)

Orphaned references in Alpha Centauri
I check pages listed in Category:Pages with incorrect ref formatting to try to fix reference errors. One of the things I do is look for content for orphaned references in wikilinked articles. I have found content for some of Alpha Centauri's orphans, the problem is that I found more than one version. I can't determine which (if any) is correct for this article, so I am asking for a sentient editor to look it over and copy the correct ref content into this article.

Reference named "MH08": From 82 G. Eridani:  From 36 Ophiuchi:  From Alpha Centauri Bb: Age discussion on page 1284 From Tau Ceti:  From Zeta Tucanae:  

I apologize if any of the above are effectively identical; I am just a simple computer program, so I can't determine whether minor differences are significant or not. AnomieBOT ⚡ 19:49, 17 October 2012 (UTC)


 * Ok, I have to say this is just a little disturbing. Next step is Cylons... ChiZeroOne (talk) 20:58, 17 October 2012 (UTC)

Hypothetical planet
It would make much more sense if the section referring to the hypothetical planet around Alpha Centauri A should probably be re-written from the context of the discovered planet around Alpha Centauri B. --EvenGreenerFish (talk) 04:34, 19 October 2012 (UTC)

Bacteria?
The claim that "the planet has an estimated surface temperature of at least 1500 K (roughly 1200 °C), too hot to be habitable for humans, yet still yielding the possibility for alien lifeforms (e.g. bacteria).[13]" does not appear to be derived from the source given [ie Eric Hand, Nature, October 16, 2012]. — Preceding unsigned comment added by 82.71.43.37 (talk) 16:55, 19 October 2012 (UTC)
 * Extraordinary claims needing extraordinary evidence. We have no evidence that life can exist at such temperatures. The dark side (likely to be much cooler) is also problematic in terms of habitability for various other reasons. Yes this is an exciting discovery but there's no need to over-hype it. 46.126.76.193 (talk) 12:25, 20 October 2012 (UTC)

I whole-heartedly agree. One doesn't need to look farther than the self-cleaning oven temperature (~900F/~500C) to realize that carbon-based life could not exist at that temperature. Also note that not even the thermophilia that live in hot springs or the hyperthermophilia that live near hydrothermal vents can tolerate temperatures much above 120C (250F). User 46.126.76.193 has already removed the offending wording, so this issue is now moot. OhioFred (talk) 21:58, 20 October 2012 (UTC)
 * I'm wondering why 1500 K excludes life (I originally asked the same thing here). In response to the point that carbon-based life could not exist at that temperature, that makes the assumption that all life has to be carbon-based. As for the references thing, "probably" isn't saying that there is life there, it's saying that life is unlikely to arise there. Wouldn't a claim that there's definitely no life there be the one that needs more evidence? Cliff12345 (talk) 22:44, 23 October 2012 (UTC)
 * Saying otherwise gives undue weight to outside possibilities that are highly speculative and unsupported by any observational evidence. There is absolutely no evidence for non-carbon based life, nor life that does not require liquid water (which cannot occur at 1500 K as this is above the critical point). 46.126.76.193 (talk) 23:28, 23 October 2012 (UTC)
 * I'd forgotten about UNDUE, what you're saying makes sense. Cliff12345 (talk) 23:37, 23 October 2012 (UTC)

Confusion.
Earlier in the article, it says that if Proxima were brighter, it'd form a visual double with AB. Later it says it would be a few moon diameters away. I don't have time to sort it out, but it's a problem.77Mike77 (talk) 02:31, 19 February 2013 (UTC)

The article contradicts itself a few times, alternately saying that Alpha Centauri is closest to Earth (false) then Proxima Centaura is closest (true). It may be that Proxima is gravitationally associated with the AB binary, but it is still too far away from AB to think of it as a triple star. There have been revisions to the article that do not address this problem. With such a fundamental issue, this article is far from "superlative", and will be merely "fair" until this glaring problem is fixed.77Mike77 (talk) 01:49, 6 April 2013 (UTC)

Mobile diagram
The numbers in the mobile diagram do not seem to make much sense. Assuming that a equals the visual separation distance. According to the article, the distance between C and AB should be 2.2°, not 2.2". The distance between A and B should be 2" to 22", not 2" to 2.2". — Preceding unsigned comment added by 212.238.236.230 (talk) 19:13, 11 March 2013 (UTC)

AU capitals...edit.
"Astronomical Unit" was changed to "astronomical unit". NASA uses capital letters...see http://neo.jpl.nasa.gov/glossary/au.html Maybe the person is using the convention for SI units, e.g. 2 newtons = 2 N, but I don't think AU is an SI unit like that. Thinking of changing it back.77Mike77 (talk) 04:43, 12 March 2013 (UTC)

Article Main Image
The current caption for this image is "α Centauri and β Centauri, with Proxima circled". Should it actually be "α Centauri-A and α Centauri-B, with Proxima circled" ? KevinTernes (talk) 21:03, 11 December 2015 (UTC)
 * No, that is actually the two separate stars, α Centauri and β Centauri. Where α Centauri is marked, it's both A & B. Tarl.Neustaedter (talk) 22:26, 11 December 2015 (UTC)

Repetitiveness
Having both a Component designations and Nature of the system seems repetitive. I suggest we fold them in together to describe the system more succinctly. Any objections? NB: discussion in the first paragraph about brightness better suited to Observation section really. Cas Liber (talk · contribs) 05:05, 21 January 2014 (UTC)

Confusing Paragraph: View from a Hypothetical Planet
I believe the paragraph is not serving purpose of a clear/proper explanation of what is happening there:


 * Assuming this hypothetical planet had a low orbital inclination with respect to the mutual orbit of Alpha Centauri A and B, then the secondary star would start beside the primary at 'stellar' conjunction.

I think this first sentence wants to say that at a moment of the planet orbit we have the 'stellar conjunction' and we consider it start (if there were humans they would most probably have a big celebration related to this, however it does not necessarily mean it would start their 'year', because the possible '4 seasons cycle' could have been totally independent from the 'stellar' conjunction and that conjunction would be every 'year' in another 'day' relative to solstices (or better said AlphaCen-AorB-stices ;)


 * Half the period later, at 'stellar' opposition, both stars would be opposite each other in the sky.

The position of the stars relative to the position of the planet depends primarily on the position of the planet orbiting around a star, so the period we are talking about is the planet's 'year'. Still we need to take into account that B has its own orbit around A and it adjusts the period between the two subsequent 'stellar conjunctions' by about Y/80 of our year, where Y is the planet's 'year' in our years (though even this is far from exact, because the stellar orbit is quite eccentric and so the apparent move of the other star on stellar sky varies from Y/40 to Y/160 in the 80 years period). Moreover, the more eccentric is the planet's elliptical orbit the less regular are the moment's of conjunctions. In the planet's year when the main axis is more-less perpendicular to line A-B connecting the star's, the period between 'stellar conjunction and opposition' could be much shorter than the second "half" (or vice versa)...

Then, for about half the planetary year the appearance of the night sky would be a darker blue – similar to the sky during totality at any total solar eclipse.

This is quite misleading, because the opposition does not last half the planetary year - it is only one extreme moment. Even if the orbit was circular, after quarter the year we would have (in ideal case of zero planet axis inclination) quarter of the day (= half of the night) dark. So the effect of B "shining" in the early morning (or late evening) would be not more impressive than our longer days during summers let's say in Germany or even better in Sweden.


 * Humans could easily walk around and clearly see the surrounding terrain, and reading a book would be quite possible without any artificial light.[105]

Yes, at the time when at least one of the stars (the planet's "sun" or the other star the planet is not orbiting around) is actually on the sky (ideally not near to horizon).


 * After another half period in the stellar orbit, the stars would complete their orbital cycle and return to the next stellar conjunction, and the familiar Earth-like day and night cycle would return.

Why stellar orbit? We are talking about the planetary orbit and its year cycle adjusted by only about Y/40-Y/160 with the stellar cycle all the time. Stars complete their cycle in about 80 years and the cycle we are talking about takes a bit more than the planet's year (about Y*(1 + Y/80) in our years).

Overall I suggest to rewrite the paragraph from scratch. Either it should just explain that sometimes B could shine at 'midnight', so that "Humans could easily walk..." and do not provide any misleading 'timing' information or it should provide correct information. I would like to hear from anybody what he would prefer. Thanks.

Eltwarg (talk) 23:06, 27 April 2014 (UTC)


 * Again. As the author who introduced this section, the information given explains the nature of the two stars in this binary system. Whilst such planets are indeed theoretical, we have to select at least a starting point. I.e. A planet similar to Earth at similar distance from the Sun. From the many frequent questions from students to amateur astronomers that are curious about the orbit and nature of the stars — especially, when compared to the sun, IMO this text is worthwhile for the sake of clarity and unnecessary debate.


 * If you think this is unnecessary, please state why. Also a star at −18.2 magnitude is 180 times brighter than the moon. so a "theoretical Earth-like planet" would be bright enough to read a book. (You can read a book via moonlight.) Frankly, the points here are trivial. Again. it is meant to present a perspective on a planet within the Alpha Centauri system. Worst, there is no descriptors of planets within double star systems. Elwarg has failed in seeing this perspective. Arianewiki1 (talk) 13:03, 31 May 2014 (UTC)

Large negative stellar magnitudes are not in common use, because such heavenly bodies are rare on Earth, so it would be difficult for a reader to find a familiar reference. Illumination in lux is commonly used and encountered for the ranges in question. — Preceding unsigned comment added by 213.35.248.23 (talk) 07:46, 20 February 2016 (UTC)

The picture
On the article's main illustration named Alpha "Centauri A/B" it is unclear if the two circles mark the actual angular diameters or not. I guess they do not, as it would require the photo to be made almost during an eclipse + the earth must lie close to the system's orbital plane. — Preceding unsigned comment added by 95.174.213.117 (talk) 18:07, 28 May 2014 (UTC)
 * Many of the pictures in this article are particularly unhelpful. It needs a good purge, keeping only the most useful of the lot or finding clearer replacements. Praemonitus (talk) 21:15, 16 March 2015 (UTC)
 * Indeed. I have gone ahead and removed a few. However, it could probably use more cleanup. --JorisvS (talk) 22:53, 16 March 2015 (UTC)

Contradictory Facts In Article
The introduction to this article states: "The separation of Proxima from Alpha Centauri AB is about 0.06 parsecs, 0.2 light years or 13,000 astronomical units (AU); equivalent to 400 times the size of Neptune's orbit."

Section 6 of the article states: "Companion: Proxima Centauri", states: " . . . Proxima, is about 15,000 AU away from Alpha Centauri AB."

Thus, the article's Introduction and Section 6 contain contradictory information regarding the distance of Proxima Centauri from Alpha Centauri AB. Please fix. — Preceding unsigned comment added by 2602:30a:2c98:cdc0:9879:f210:412a:ad1d (talk • contribs) 06:30, 13 March 2015‎

Good point. Referenced text is preferred to general text in introduction, so changed to 15,000. Thanks, good pick-up!! Arianewiki1 (talk) 14:02, 13 March 2015 (UTC)

Planet v. Exoplanet
JorisvS Definition, as stated in Wikipedia itself.

"An exoplanet or extrasolar planet is a planet that does not orbit the Sun and instead orbits a different star, stellar remnant, or brown dwarf."

Also it the same page says; "The nearest known exoplanet, if confirmed, would be Alpha Centauri Bb, but there is some doubt about its existence. "

Oxford dictionary on-line defines: "A planet which orbits a star outside the solar system." 

For example, the IAU states; "The first exoplanet tentatively identified around the second brightest star in the triple star system, Alpha Centauri, is accordingly called Alpha Centauri Bb. If an exoplanet orbits both of the stars in a binary system, its name can be, for example, Kepler-34(AB) b." 

I can access more than another dozen references to support this.

Planets around other stars are exoplanets and not planets. Hence, definition of planets within the Solar System, as edited.

Please get your facts right before editing, and revert my edit please.

(Note; The alternative form are 'solar planets' and 'extra-solar planets', actually. If you were to discuss this with the IAU, you will find control is with WGEP (Working Group on Extrasolar Planets) in Commission 53 'Extrasolar Planets', which has existed since August 2006.

Please show evidence of the contrary statement. Thankx. Arianewiki1 (talk) 17:55, 17 March 2015 (UTC)
 * "An exoplanet or extrasolar planet is a planet that ...". Exactly what I said! All exoplanets are planets, but not all planets are exoplanets. "Planet" does not mean specifically those eight in the Solar System. Wherever "planet" is correct and clear, there is no need to use "exoplanet". In "The nearest known exoplanet, if confirmed, would be Alpha Centauri Bb ...", saying "exoplanet" is necessary because "the nearest known planet" means something distinctly different. As for the IAU definition, they just didn't want to deal with exoplanets, where our knowledge is far less. --JorisvS (talk) 18:20, 17 March 2015 (UTC)


 * What? Can't you read the above text?


 * Another Definition: "The definition of planet, since the word was coined by the ancient Greeks, has included within its scope a wide range of celestial bodies. Greek astronomers employed the term asteres planetai (ἀστέρες πλανῆται), "wandering stars", for star-like objects which apparently moved over the sky."


 * Exoplanets don't wander across the night sky, but the planets of the Solar System do, so the term 'exoplanet' has been used.


 * IAU says;
 * "A planet is any object in orbit around the Sun with a diameter greater than 2000 km.
 * A planet is any object in orbit around the Sun whose shape is stable due to its own gravity.
 * A planet is any object in orbit around the Sun that is dominant in its immediate neighbourhood."


 * Also. Exoplanets don't orbit the sun, now do they?


 * As for " As for the IAU definition, they just didn't want to deal with exoplanets, where our knowledge is far less." So what. This statement is irrelevant. This is not reference that supports the use of 'exoplanet' not 'planet'. I.e. YOUR opinion. Please give evidence for this statement.


 * Either come up with actual evidence of the contrary statement, which counteracts this statement (and is not based on your own opinion), or revert. Thanx.. Arianewiki1 (talk) 18:46, 17 March 2015 (UTC)
 * Seriously, you're going to include the Ancient Greek definition to argue for your position?? What is seriously so hard about simply reading both the definition you've given above or the one at exoplanet, "An exoplanet or extrasolar planet is a planet that does not orbit the Sun and instead orbits a different star, stellar remnant, or brown dwarf.". These state crystal-clearly that an exoplanet is a planet! Moreover, Planet says "More than a thousand planets around other stars ("extrasolar planets" or "exoplanets") have been discovered in the Milky Way". And as for your naive legalistic reading of the phrasing of the IAU definitions: read Exoplanet. That exoplanets are also planets is emphatically not my opinion. And if you don't want to believe me and the articles to which I refer, why don't you take it to WP:Astronomy and see the reactions from other editor. --JorisvS (talk) 21:00, 17 March 2015 (UTC)


 * Again, you are interpreting this incorrectly, and is it is clear you have need to provide a reference that supports your claim. The IAU definitions are absolute, agreed by international agreement. I.e. You earlier stating "As for the IAU definition, they just didn't want to deal with exoplanets, where our knowledge is far less.", is proof your arguments are plainly flawed. By your logical, dwarf planets are planets too, which is clearly wrong.
 * Whether exoplanets are planets or not relevant actually, because the adopted definition exists to distinguish between them. I.e. planets orbit the sun, while exoplanets orbits other stars. Why ignore it? They are planetary bodies, but strictly, they are not defined as planets. Again, you still have not provided ANY independent source that contradicts this. I.e. The IAU definitions are verifiable and cited sources. Unless you can really provide some relevant verifiable source,  WP:Astronomy is irrelevant, UNLESS you can provide verifiable sources as citations to contradict this. So far you have provide none. Arianewiki1 (talk) 22:05, 17 March 2015 (UTC)
 * You're basically claiming all our articles on this topic are completely wrong in this respect (even though they're sourced and stable). The definitions (including the one you came with above!) say what I've been telling you the whole time. All the necessary references are in the articles, but you haven't actually come with one that supports your position. Yet somehow you want me to find (other?; there are already in the articles) references to support my position. It is you who should find references that actually support your position. And try to get your logic straight, nowhere did I claim that dwarf planets are also planets. You wouldn't be downplaying WP:Astronomy if you didn't know you'd find yourself arguing against lots of people, not just me. --JorisvS (talk) 22:39, 17 March 2015 (UTC)


 * All references are these…


 * 1) Definition, as stated in Wikipedia itself.
 * "An exoplanet or extrasolar planet is a planet that does not orbit the Sun and instead orbits a different star, stellar remnant, or brown dwarf."


 * 2) Also it the same page says; "The nearest known exoplanet, if confirmed, would be Alpha Centauri Bb, but there is some doubt about its existence. "


 * 3) Oxford dictionary on-line defines an exoplanet as: "A planet which orbits a star outside the solar system."


 * 4) For example, the IAU states; "The first exoplanet tentatively identified around the second brightest star in the triple star system, Alpha Centauri, is accordingly called Alpha Centauri Bb. If an exoplanet orbits both of the stars in a binary system, its name can be, for example, Kepler-34(AB) b."


 * All these are obvious cited references. Yet you have yet to provide a single cited reference!!!


 * Plainly if "An exoplanet or extrasolar planet is a planet that does not orbit the Sun and instead orbits a different star,…" Then a planet orbits the Sun, and an exoplanet does not orbit the Sun. They may be planetary bodies, but they differ in definition because they orbit either the sun or other stars. Arianewiki1 (talk) 23:07, 17 March 2015 (UTC)


 * Your statement: "You wouldn't be downplaying WP:Astronomy if you didn't know you'd find yourself arguing against lots of people, not just me. -" Please find actual evidence to support this statement please. I.e. You are an individual, and cannot argue for other peoples point of view nor make statements of 'fact' based on assumptions. This is plainly falsifying consensus. Also WP:Astronomy is quite irrelevant, as fact here is based on cited or valid references. I.e. Logically, if Alpha Centauri has a planet orbiting this star, then the term exoplanet applies NOT planet. You need to provide a specific reference that says otherwise. (not what you just think is true.) Arianewiki1 (talk) 23:24, 17 March 2015 (UTC)

Ariane, your last quote clearly states that exoplanets are planets. I'm sorry you're having difficulty understanding your sources, but they're quite clear.

As for when to use which term, "exoplanet" is usually used when plain "planet" would be ambiguous. Once in the context of a particular planetary system, as in this article, "planet" is all that is needed. — kwami (talk) 23:13, 17 March 2015 (UTC)
 * No. Not according to the IAU. Please state a cited reference(s) that your statement is true. Arianewiki1 (talk) 23:27, 17 March 2015 (UTC)


 * You keep demanding sources, so provide your source. We are not contradicting the 2006 IAU definition of "planet"; if you have some other IAU source, please share. — kwami (talk) 23:51, 17 March 2015 (UTC)


 * To revert an Article edit, you should cite reference(s) that validate the errors, especially when seeking consensus. I have already provided the citation that support this, but you have reverted without proper discussion on this talk page. Please state a cited reference(s) that your statements are true. Arianewiki1 (talk) 23:35, 17 March 2015 (UTC)


 * You don't seem to understand how things work around here. Please read WP:BOLD.  Since they're your edits, it's up to you to justify them, and to convince the rest of us.  As it is, you've provided refs that disprove your claims.  (That is, all we need to do to provide refs is to repeat the refs that you gave!)  If you continue to WP:edit war, I will ask to have you blocked for disrupting the encyclopedia.  — kwami (talk) 23:44, 17 March 2015 (UTC)


 * The page has now been protected, which has probably saved you from being blocked. Please consider your logic:  You're arguing that exoplanets are not planets because exoplanets are planets!  — kwami (talk) 23:47, 17 March 2015 (UTC)


 * Please stop making false statements. I.e. "You're arguing that exoplanets are not planets because exoplanets are planets!" That is not true. I am arguing the definition of exoplanets and planets, which are not the same definition. A planet that orbits another star is called an exoplanet. Please give citations to the contrary. (You haven't even done that.) Also my last edit followed the usage adopted in the cited references, not my own. If it is in the article title, is should follow that usage. Also note the IAU has defined the use of exoplanet, and is currently involved in their naming. [] Note: WP:edit war here also applies to you too. Arianewiki1 (talk) 00:03, 18 March 2015 (UTC)
 * Do you even understand what you're saying?? "A planet that orbits another star is called an exoplanet.": Here you're, again, saying that exoplanets are planets. That sentence would be self-contradictory if exoplanets were not planets! --JorisvS (talk) 01:35, 18 March 2015 (UTC)


 * Actually, I'm saying "An exoplanet is a planet that orbits another star (i.e., not the Sun)." (See below.)


 * It is the definition that is important here. Exoplanets orbit other stars, not the sun!!!


 * Yet you unbelievably change under the title "Designations for exoplanets", that "Currently, according to the IAU, there is no agreed system for designating planets orbiting around other stars.". This statement is obviously false. Arianewiki1 (talk) 01:57, 18 March 2015 (UTC)
 * Exoplanets do orbit other stars, not the Sun. All exoplanets are planets, but not vice-versa, just like all apples are fruits, but not all fruits are apples. Why do I remove exo from ""Currently, according to the IAU, there is no agreed system for designating planets orbiting other stars."? Because "exoplanet"="planet orbiting another star", which means that "exoplanets orbiting other stars" is a tautology. It is sufficient to say "Currently, according to the IAU, there is no agreed system for designating planets orbiting other stars." OR "Currently, according to the IAU, there is no agreed system for designating exoplanets.". --JorisvS (talk) 02:06, 18 March 2015 (UTC)


 * Here "designating planets" does not equal "definition" of planets or exoplanets. Here "designating planets" is actually the current programme to name or class these exoplanets!! We are talking about "astronomical / scientific definitions", and how they are specifically defined. Planets from the perspective of sun or the stars behave differently and are discovered differently by differing methods. There are many good reasons to do this, and not just because they sizeable planetary bodies are made of rock, ices or gas. Arianewiki1 (talk) 03:00, 18 March 2015 (UTC)
 * Never did I say that "designating planets"="definition". Just because we need distinct methods to discover exoplanets (which is simply due to their distant location) does not mean that there is any meaningful physical difference that would warrant "exoplanet"≠"planet". Time and again here you've said that exoplanets are planets (e.g. "An exoplanet is a planet that orbits another star" literally says that exoplanets are planets), only to then try to use that to deny the very thing you've said. Your argument is logically incoherent and wrong. --JorisvS (talk) 03:10, 18 March 2015 (UTC)


 * The desperation here beggars belief. 'exo-' prefix means outside, and the term literally means a planet outside the solar system. Again. the scientific definition is more important, else why bother making a difference between planetary types. I.e. Let's call them all planets, and be done with it. Let's be foolish and just totally ignore the IAU and all the associated institutions, and pretend JorisvS is the guru of astronomical on all this. So when +5000 of them are named by the IAU, general confusion will ensue, as we will not know where or why they are placed. Who cares if we cannot differentiate between the brown dwarfs, or the hot Jupiters, massive Neptunes, gas dwarfs or super-earths. Yet there are big difference between the two designations are much uncertainty, and if you read the exoplanet page, the reasons are plainly stated.
 * Yes, the exo- designation hasn't been added there for fun, and when the IAU decides of a scientific definition, aligned on expertise and knowledge, we get this madcap libertines (like those who want to resurrect Pluto) who feel these things should be made on some weird democratic principle - made worse by openly sledging the IAU without wisdom to understand why. (Didn't you think someone notices continuous edits of Pluto page?]
 * Again. Show references that refute the difference between planet and exoplanet, or even why it is necessary to have a term "exoplanet." According to your own twisted logic, it is just unnecessary. Yet you still haven't show even one single example!! Arianewiki1 (talk) 05:39, 18 March 2015 (UTC)
 * Again you're interpreting me way off. Of course, "exoplanet" is a useful term, I have never claimed it isn't. You've provided a number of quotes that say exoplanets are planets, yet you're trying to use them for the exact opposite of what they're saying (makes perfect sense...not). And if your claim, for you have given no actual sources and actually opposite quotes, is right, our Exoplanet and Planet articles, and the sources they are based on, are dead wrong (and no, I didn't write them). --JorisvS (talk) 09:30, 18 March 2015 (UTC)

——

Well under the Exoplanets Data Explorer, which collects all the data on exoplanets, it plainly says straight out in FAQ.

"An exoplanet is a planet that orbits another star (i.e., not the Sun)."

Under Wikipedia's own |Definition IAU "The official definition of "planet" used by the International Astronomical Union (IAU) only covers the Solar System and thus does not apply to exoplanets." See also Astronomical naming conventions

The iAU formally says ;

"A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit."

They further say "Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation "planets". The word "planet" originally described "wanderers" that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information."

That new definition defines exoplanets.

This evidence cannot be more obvious. Unless you have a different written contrary definition from another source, and can also cite it, then this should be then used as it applies to both WP:MOS and WP:NASTRO. All the IAU definitions are the primary absolute source here, and are recommended in syntax and definition of astronomical bodies.

In the end, this follows the conventions here, and should be adopted as per my given WP:GF edits.

If existing definition of Wikipedia (and the IAU) are not adequate, especially for users who properly apply it, consensus is not required. (Else change the definitions.)

Furthermore, these statements by others above;


 * ""Planet" does not mean specifically those eight in the Solar System."


 * "As for the IAU definition, they just didn't want to deal with exoplanets, where our knowledge is far less. "


 * "These state crystal-clearly that an exoplanet is a planet!"


 * "You're basically claiming all our articles on this topic are completely wrong in this respect (even though they're sourced and stable)."


 * ""You wouldn't be downplaying WP:Astronomy if you didn't know you'd find yourself arguing against lots of people, not just me.""


 * "As for when to use which term, "exoplanet" is usually used when plain "planet" would be ambiguous."


 * "Once in the context of a particular planetary system, as in this article, "planet" is all that is needed."


 * "You're arguing that exoplanets are not planets because exoplanets are planets!"


 * "As it is, you've provided refs that disprove your claims."

These statement are all false. I would possibly suggest you should strike them out.

Note: As for "If you continue to WP:edit war, I will ask to have you blocked for disrupting the encyclopedia." stated by kwami. I perceive this as a direct threat against WP:GF and WP:CIV. Your own two reverts of the text and actually avoided to gain consensus by disregarding this discussion, which I had instigated on JorisvS revert. So far not one cited reference has been given here by JorisvS nor kwami to support the case. I request you kindly strike this offending remark immediately. Thankx. Arianewiki1 (talk) 01:50, 18 March 2015 (UTC)


 * Again, you're providing our sources for us, as all of your sources contradict you. I don't know how to address what appears to be functional illiteracy.  (That's not an attack.  When you present a source that defines 'planet' as we do, and then claim it says the opposite, I can only conclude that you are not able to parse academic written English.  Or even Wikipedia articles, for that matter.)  As for the IAU, they specifically say that they only address the Sol system. — kwami (talk) 01:57, 18 March 2015 (UTC)


 * Plainly you just don't get it. "An exoplanet is a planet that orbits another star (i.e., not the Sun)."
 * So quite logically. Definition of Alpha Centauri is called a exoplanet. The term is used not to confuse a planetary body orbiting the sun.
 * If a planet orbits another star, it is defined as an exoplanet.
 * If a planet orbits around the sun, it is defined as a planet.
 * How can a planet orbit around a distant star then be a planet?
 * It ain't illiteracy, is plainly logical…
 * So which statement above is therefore false, then? 02:10, 18 March 2015 (UTC)


 * The false statement is "if a planet orbits around the sun, it is defined as a planet". As for your question, "how can a planet orbit around a distant star then be a planet?", simple:  because, as you just said, it's a planet.
 * I'll give an analogy to your argument: A rocky planet (formed inside the frost line) is a terrestrial planet.  Earth is a terrestrial planet.  Therefore, Earth is not a planet.  That is spurious logic.
 * Or, to paraphrase you above, An exoplanet is a planet that orbits another star. So, quite logically, an exoplanet is a planet because your definition assumes it as a planet! — kwami (talk) 02:34, 18 March 2015 (UTC)


 * Again, plainly wrong. As I said above;"We are talking about "astronomical / scientific definitions", and how they are specifically defined. Planets from the perspective of sun or the stars behave differently and are discovered differently by differing methods. There are many good reasons to do this, and not just because they sizeable planetary bodies are made of rock, ices or gas." Where they reside is what's important here. Arianewiki1 (talk) 03:04, 18 March 2015 (UTC)


 * I have no opinion on this issue, and my only involvement is protecting the page to stop the edit-warring, which is not an endorsement of the current version. StringTheory11 (t • c) 02:06, 18 March 2015 (UTC)


 * I didn't expect otherwise. Just wanted to show this is being properly discussed on the talk page here, and not expecting endorsement nor condemnation. Arianewiki1 (talk) 02:14, 18 March 2015 (UTC)

(Exo)planet in the intro
The intro contains a whole paragraph about the confusion over whether a planet exists or has been detected in the system. Since this is so spurious at the moment, I think the whole para should be removed from the intro. The intro should summarise the established facts of the article. Ashmoo (talk) 12:57, 24 March 2015 (UTC)
 * It was way too detailed for the lead, even if no one would doubt its existence. However, regardless of whether doubt exists over its existence, it has been notable enough to merit a short mention in the lead, at least at present. I have pruned it. --JorisvS (talk) 14:18, 24 March 2015 (UTC)
 * Great, your version looks perfect to me. Ashmoo (talk) 15:07, 24 March 2015 (UTC)
 * I have no disagreement with this edit. Arianewiki1 (talk) 16:16, 24 March 2015 (UTC)

Alpha Centauri ABb and the hypothesised orbital period
It says in the, "Other possibly detected planets", section of this Wikipedia article, that Russian scientists have discovered a planet that would, "...be located at a distance of 80 AU and would orbit both stars with an orbital period of about 100 years." But, if a planet was orbiting Alpha Centauri AB at 80 AU, in a reasonably circular orbit, it would take at least 500 years to complete. Even a highly eccentric orbit would take about 200 years, 180 years at minimum if the semi-major axis was 40 AU and then the planet would either be grazing the stars or going between them. So, it is hard to take seriously the 100 year figure quoted, unless it's a rogue planet travelling at a faster velocity and then it's not actually in orbit around the stars.

Also neither does this Wikipedia article, or the reference source given by it, say where the source of the data, the Russian scientist used to discover the planet, came from. You obviously can't see Alpha Centauri from the Pulkovo Observatory in St. Petersburg. So, the Russian scientists must've analysed data obtained from some other observatory, but from where?

I quickly glanced at all the presentations made at the "Journees 2014", held by Central Astronomical Observatory of the Russian Academy of Sciences in St Petersburg, Russia. The conference presentations can be viewed at http://www.gao.spb.ru/english/as/j2014/programme.htm. But, only one presentation made there, "Shevchenko I. (invited) Resonances in the Solar and exoplanetary systems. - Presentation", seems to refer to Alpha Centauri at all and it's not, as far as I can tell, even talking about a planetary discovery there.

The only evidence given in this Wikipedia article, for the circumbinary planet discovery, is a reference to a "TASS Russia News Agency" report and not a scientific paper. Is that really a reliable enough source to trust here? — Preceding unsigned comment added by 86.176.162.206 (talk) 02:30, 1 April 2015 (UTC)
 * It is supposed to have been calculated that should be there, without much detail about why it should be there. And then the second source talks about the possibility of liquid water without going into the necessary detail to understand what is going on. On the one hand is it impossible to see, yet somehow there has been a spectral analysis. I, too, calculate that at a semi-major axis of 80 AU it should have an orbital period of ~500 years. Orbital period does not change with orbital eccentricity, only semi-major axis. I cannot locate any scientific article about this. It smells like a hoax. --JorisvS (talk) 09:33, 1 April 2015 (UTC)

Alpha Centauri B's rotational period
From the main text:

"The projected rotational velocity ( v·sin i ) is 1.1 ± 0.8 km·s−1, resulting in an estimated rotational period of 41 days. (An earlier, 1995 estimate gave a similar rotation period of 36.8 days.)"

Yet the infobox says that the rotational period for B is 47 days.

Both the text and the box agree that the rotational period for A is about 22 days (although the infobox allows some variability: "~22.5 ± 5.9 days"

Is more consistency possible here? 108.246.206.139 (talk) 05:27, 24 June 2015 (UTC)

Redundant Sentence?
In the section, Companion: Proxima Centauri, the last sentence in the first paragraph is, "It is not yet certain whether Proxima and Alpha Centauri are truly gravitationally bound."

Isn't this sort of redundant? I'm pretty sure people could get that by the time they even reach that sentence. I mean, it does say, "However, it is also possible that Proxima is not gravitationally bound and thus moving along a hyperbolic trajectory with respect to Alpha Centauri AB", after all, earlier in the paragraph.

Confusing Part of Talk Page
Wouldn't it be better if the reference at the bottom of this talk page were put into its own section? It's kind of confusing to have it be right there, without even a full line break to separate it. Honestly, before I figured out it was someone else's reference, I thought I had somehow put a link in my post. Seems like just putting it in a separate References section would be an easy solution to an annoying minor issue, that's all. :/ — Preceding unsigned comment added by SarahTehCat (talk • contribs) 00:34, 22 August 2015 (UTC)

Rewrite the lede
The lede seems to WANT to be confusing. AC is a binary system of 3 stars? No, its not. The system appears as a single VISIBLE star (to the naked eye) with two stars contributing to its VISIBLE brightness. The first paragraph of the Nature and Components section does a better job at introducing the subject than the contradictory lede. Alpha Centauri may refer to the stellar system (gravitationally bound, composed of two or probably 3 stars as well as possibly one or more planets (although the latter fact has been recently questioned). And it refers to a visible sky object, a "star". In addition, I wonder if it is established FACT that it is closest to Earth (that is, that Proxima Centauri is), rather it is the closest star KNOWN. (I believe there was some work published in the last year or two placing some constraints on the existence of stars near-by that have remained as yet undetected - possibly down to the brown dwarf category, which are generally not considered "stars".) Anyway, Alpha Centauri may refer to the visible star or the star system. The visible star is composed of two stars and Proxima Centauri, Alpha Centauri-C, is probably the third star in that star system but, although we predict it to be gravitationally bound, it is not visible to the naked eye so not part of the visible star. And please remove the backward phrasing of its relative brightness (note: "relative") when its described as "only fainter than". Use plain English. Only two stars in the night sky appear brighter. But you should also note that it is a Southern Sky star, and not visible from above latitude X in the Northern Hemisphere, and that it is therefore normally the second brightest star in the southern sky, after Canopus, and is part of the constellation Centaurus. (Not sure what X is, 45° ? ) Any reference to brightness should always clarify that it is apparent brightness, not absolute magnitude, that we are talking about, imho. Perhaps I'm being too picky there.216.96.76.79 (talk) 08:29, 30 August 2015 (UTC)


 * Ok, I tried rejigging it like so. I think we can leave out "closest known star" as it is extremely unlikely anything larger than a small brown dwarf (and hence nonstellar) will be found. Cas Liber (talk · contribs) 10:02, 30 August 2015 (UTC)


 * Let's see: 1) Alpha Centauri is a system consisting of three stars, A, B, and C (Proxima), which is most likely gravitationally bound and, if not, is still associated with A–B. The point of light in Earth's sky is just a consequence of the existence of this stellar system and article's are about stars and stellar systems, not 'points of light in Earth's sky', which is not something distinct, but simply what we can see of it with the naked eye here. 2) There are no stars or brown dwarfs closer to the Sun than Proxima, else WISE would have detected them (it has even ruled out Tyche).
 * You're quite right, though, that it should be crystal clear at all times whether something is the apparent or absolute magnitude. I have improved this. --JorisvS (talk) 10:20, 30 August 2015 (UTC)


 * There is a problem with all this. The implication now in the lead is that Proxima contributes to what is seen with the naked eye.  It doesn't.  It would be clearly separated from AB if it were actually visible to the naked eye.  The "point of light" that is seen is not even marginally affected by Proxima's feeble light. This is actually explained, quite well I thought, further down the article.  To give you some context the article itself describes the separation as "four times the angular diameter of the full moon", not even close.  Lithopsian (talk) 13:11, 30 August 2015 (UTC)
 * Aah. good point. Will sleep on it as midnight here. Cas Liber (talk · contribs) 14:02, 30 August 2015 (UTC)
 * Proxima Centauri has its own featured article. It is probably best to treat it as a separate object, with a mention that it might be physically associated.  It is two degrees away from Alpha Centauri, over a fifth of a light year away.  I gave this a quick look over when the original talk posting was made and I thought the lead was reasonably informative and accurate.  Perhaps it doesn't make sense to go back after all the improvements today, but certainly worth a look back at that version with a new point of view.  Lithopsian (talk) 19:33, 30 August 2015 (UTC)
 * Why? It is most likely part of the same system. Just because it happens to be so close it can be seen far from AB. Of course because we have the separate article, we do not need to cover it in more detail than just a summary. --JorisvS (talk) 10:28, 31 August 2015 (UTC)
 * The problem is that the lead now implies (actually states pretty strongly) that while Alpha Centauri appears as a single naked eye object, it consists of three stars. It doesn't.  The system may (or may not) gravitationally consist of three stars, but visually Alpha Centauri consists of A and B, seen as a single object without considerable optical assistance.  We shouldn't claim that a star two degrees away, regardless of what that translates to in physical distance, is part of that naked eye object.  Lithopsian (talk) 10:38, 31 August 2015 (UTC)
 * You're right about that, of course. The problem is in the definition, which is currently a looking-at-the-sky approach. I'll take a crack at it. Let's see what we can make of it. --JorisvS (talk) 11:12, 31 August 2015 (UTC)

Apparent magnitude, -0.27 or -0.29?
Few scientific papers or catalogues quote a combined visual apparent magnitude for Alpha Centauri AB. Instead there are separate values for A and B. The combination is a well-defined mathematical operation, and I don't think it contravenes WP:NOR. Until recently, this article showed the value -0.27, with a reference to Burnhams Celestial Handbook (it is on page 549). Burnham also gives individual magnitudes for A and B, at -0.04 and +1.17 respectively. Unfortunately that doesn't combine to -0.27. Coincidentally (?), the individual magnitudes shown in the article were +0.01 and +1.33, which do combine to -0.27. These values were not cited, but do match the values currently at Simbad, derived from Ducati 2002.

So far, so good. Then I came along and added references for the individual magnitudes. I used the Bright Star Catalogue since I was looking at it for the Brightest Stars List article. It is an older source but widely referenced. The A and B values were -0.01 and +1.33, combining to -0.29. User:JorisvS changed the combined value to -0.27 (with a web-page citation), but not the individual magnitudes. This edit got overwritten by some subsequent edits, so it now says -0.29 again and is consistent with the individual magnitudes. However there is a case for using the newer reference and going back to -0.27, with individual magnitudes of +0.01 and +1.33. I generally use the newest available dedicated photometry, which is usually what Simbad links to, in this case Ducati 2001.

Any thoughts? Lithopsian (talk) 13:31, 1 September 2015 (UTC)
 * I just saw that the source cited then did not give the combined value. Looking for a citation, I found one at the German Wikipedia, but that says −0.27, so I changed it. I'm fine with using a newer reference for the individual values and −0.29, as long as a note is added explaining the required calculation. --JorisvS (talk) 15:04, 1 September 2015 (UTC)
 * Well that ended up being a lot of work. Turned out much of the starbox data was out of date or not referenced, and there were several formatting problems.  Should all be fixed, but definitely worth checking over.  I used Ducati 2001, A=+0.01, B=+1.33, combined magnitude -0.27. Lithopsian (talk) 16:44, 1 September 2015 (UTC)

Starbox image
What is that? Does that tell anyone anything? It isn't even nice eye candy. Surely we can do better. Lithopsian (talk) 16:46, 1 September 2015 (UTC)
 * Gone. Replaced with something hopefully more informative, as well as quite attractive. Lithopsian (talk) 14:50, 3 September 2015 (UTC)

How far away is Alpha Centauri?
Seems like there should be a well-known and widely-accepted value, but it appears not. Recent research papers quote various values from 1.33 pc to 1.35 pc, or just 1.3 pc or 1.4 pc. This isn't an entirely trivial difference for such an important star. The table in the article summarises the relevant parallax measurements. The most import are: Perryman (1997) ,the original Hipparcos reduction; Söderhjelm (1999), a refinement of the original Hipparcos reduction using binary orbit data; and van Leeuwen (2007), the new Hipparcos reduction. The Söderhjelm reduction is the most widely cited value, and was certainly the most reliable prior to 2007. However, even after 2007, the new Hipparcos reduction is largely ignored. Unfortunately I couldn't find a single source that says why, so I don't know if there is a good reason why Söderhjelm is preferable or if lazy researchers are just cut'n'pasteing from the last paper they wrote. Söderhjelm makes useful refinements to the original Hipparcos reduction and obtains an impressively small margin of error, but obviously doesn't take into account the systemic sources of error analysed in the new Hipparcos reduction. The existence of unaccounted for sources of error in at least some reductions is clear from the non-overlapping error ranges of the various reported parallaxes. Right now this article contains the van Leeuwen (2007) parallax values, including the rather inaccurate separate value for component B (not calculated in other reductions due to the known inaccuracy), and the plain distances derived by the starbox. That means component A shows a distance somewhat smaller than most other sources (eg. 4.32 ly vs 4.37 ly) while component B is showing a clearly aberrant distance of 4.1 ly. Seems like at least the component B value should be forced manually to something sensible, perhaps with a footnote? Lithopsian (talk) 15:20, 3 September 2015 (UTC)
 * Since the two components orbit one another, shouldn't they both have a range of distances for the Earth? Kortoso (talk)
 * The orbit is tiny by comparison, less than 0.001 light years across. Lithopsian (talk) 22:27, 1 October 2015 (UTC)

New data
A paper published in January 2016 revises the parallax, masses and orbital parameters: Parallax and masses of α Centauri revisited⋆ Dimitri Pourbaix1,⋆⋆ and Henri M. J. Boffin. Should we update the article with the new numbers?--agr (talk) 12:38, 28 August 2016 (UTC)

Inclination?
The Infobox states that the inclination is "79.205 ± 0.041°". It appears to indicate that this is the inclination for both A and B components. Is that likely? I have to assume that this is the value for A and that the inclination for B is missing.

Or am I missing something?12.222.8.178 (talk) 18:32, 28 October 2015 (UTC)


 * It refers to the orbit. By definition, an orbit with two components is in a plane, that entry is defining the inclination of that plane. Tarl.Neustaedter (talk) 19:28, 28 October 2015 (UTC)
 * So it refers to the orbit of A around B and vice versa. Thanks! Kortoso (talk) 19:51, 28 October 2015 (UTC)

Age
The source used to cite the the ages of A and B, has two very different ages for A and B, which are now also in the infobox. I would expect A and B to be the same age. Is it realistically possible for the two components of a fairly close binary to have such drastically different ages? --JorisvS (talk) 11:56, 17 February 2016 (UTC)
 * As I read that article, I understood it to propose a method for calculating ages, but it has large error margins, and does not claim certainty. I find the below paragraph particularly relevant, about table 13, where t1 and t2 for A and B are 6.6/4.2 (A) and 5.2/6.5(B).
 * Estimated ages using our methods are listed in the final two columns of Table 13. The first column of ages ( t1 ) are from using the revised activity-age relation (x 3.2.2, eq. [3]). The second column of ages ( t2 ) are those inferred from converting the chromospheric activity levels to a rotation period via the Rossby number and then converting the rotation period to an age using the revised gyro relation (x 4, eqs. [5] Y [8] and [10] Y [12]). The final column of ages t2 are the preferred age estimates. The inferred activity age for the extraordinarily active zero-age MS star AB Dor is  1 Myr and clearly in error (apparently by 2 orders of magnitude; Luhman et al. 2005). As AB Dor painfully illustrates, the uncertainties in the inferred ages for the very active stars (log R0 > HK 4:3) are large ( 1 dex; e.g., Table 9). A conservative estimate of the typical age uncertainty is  50% for the preferred ages of the lower activity stars.
 * As I understand it, at best, those ages are inaccurate to within 50%, certainly not enough to claim the stars were created at different times. Tarl.Neustaedter (talk) 00:42, 21 February 2016 (UTC)
 * Giving these values without uncertainties is extremely misleading, because we can indeed expect them to be the same age. I don't know if we can use the current source properly for that; they give such a top-of-the-head figure. Do you? Else, we should try to find a different article. --JorisvS (talk) 09:16, 21 February 2016 (UTC)

Toliman
I had a hard time figuring this out, but Tolimân is apparently Golius' (1669) rendition of what Al-Farghani mentions as a native Arabic name of the Centaurus constellation, apparently (not translated by Golius but according to Kunitzsch 1961) corresponding to ظلمان  Ẓulmān "ostriches". Note that neither Al-Farghani nor Golius give this as a name of the star Alpha Centauri, it is mentioned as an alternative name of Centaurus. It is unclear when and where this was first used as a name for the star, but Kunitsch in the 1976 article states that according to his knowledge, this alternative name had only currency in German-language literature, so I'm going to assume it came up in the 1960s in German astronomical almanacs and/or astrological literature. Indeed, all pre-1990 references known to google books are German. The earliest mention of the name in English-languge literature to be found dates to 1992. Also, the entire role of this name in English or German literature is "here is a list of alternative names of Alpha Centauri". Nobody actually ever uses this as an actual name to refer to the star. It seems to be part of a 1990s fashion to give as many "multicultural" names of stars as humanly possible. --dab (𒁳) 15:38, 8 May 2016 (UTC)
 * actually, correction: there is an opaque tradition of English-language references invoking a fake Hebrew etymology of the name. This was apparently the original idea of one Frances Rolleston in a work called MAZZAROTH, or, the CONSTELLATIONS published in 1863. This never comes up in actual astronomical literature, which seems to import the name from German, but it shows up now and again in Hebrew-mysticism/occultist literature. --dab (𒁳) 15:41, 8 May 2016 (UTC)

Sun and constellations viewed from Alpha Centauri
The section about the night sky seen from AC states that "Sirius lies less than a degree from Betelgeuse in the otherwise unmodified Orion", but if one checks with the simulation picture of this night sky, Orion actually looks quite tilted. Relative to Orion's Belt, Betelgeuze is roughly where Bellatrix would be seen from Earth, and the inclination of the belt looks fairly different, too. It's as if our starry Giant has been tilted, even wrung around (compare with any normal map/sketch of Orion and you'll see what I mean).

This is puzzling because the lead stars in Orion are much more distant than many other in the night sky, so the whole figure shouldn't be that much affected by a distance of four light years on the end of the viewer. Bellatrix is almost three times closer than Betelgeuze, but it's still hard to see that this would make much difference to its position in the sky (it's still 240 light years away) and change the constellation in this way. The belt stars are farther away than either of them. Strausszek (talk) 03:53, 20 August 2016 (UTC)
 * What you're noticing (the stretching effect) is almost certainly the result of projecting a spherical surface onto a flat screen - fitting both the Sun and Sirius into the image results in serious spherical aberration away from the center of the projection. You are correct, Orion's stars are so far away that from Alpha Centauri, that constellation would look almost un-altered. If you want to see Orion as it would be seen from there, you'd have to get Celestia and re-project that image centered on Orion, rather than having it off to the side of the image. Tarl N.  ( discuss ) 04:10, 20 August 2016 (UTC)


 * Ahh, projection distortion! Just like in most maps of a large chunk of the earth's surface (South America, New Zealand and Australia can look really weird on some world maps). You're right of course, I just didn't realize that the section of the sky in the picture was so large and that Orion was in a corner. Since it's on the celestial equator of the sky (at least viewed from Earth) unconsciously one expects it to come out "right" in any map. Thanks: Strausszek (talk) 15:31, 20 August 2016 (UTC)

Revised masses
To whomever maintains this article:
 * "The components are thus a bit more massive than previously thought (1.13 and 0.97 M⊙ for A and B, respectively). These values are now in excellent agreement with the latest asteroseismologic results."

Per: Praemonitus (talk) 15:02, 31 August 2016 (UTC)

Redundant sentence
The article says, " Because the distance between the Sun and Alpha Centauri AB does not differ significantly from either star, gravitationally this binary system is considered as if it were one object."

This describes all true binary systems, and it does not explain any important property of Alpha Centauri. 2600:1000:B11B:79CF:69F0:EA5B:67C9:8A79 (talk) 15:17, 27 September 2016 (UTC)
 * This is in the second paragraph of Alpha Centauri, in a discussion of why designations often consider "C" a separate object, but A&B are generally listed as a single object. It's a clumsy statement, and could certainly stand re-wording, but the essence is that for practical purposes the C component is often listed as a separate object (it's objectively nearer and has a really wide angular separation), while the AB components (like most binary stars) are usually listed as a single object together. Any good ideas on how to rephrase it? Tarl N.  ( discuss ) 16:02, 27 September 2016 (UTC)

Binary system
Some of the text in this section (https://en.wikipedia.org/wiki/Alpha_Centauri#Binary_system) is redundant. For instance: "From the orbital elements, the total mass of both stars is about 2.0 M☉—or twice that of the Sun. The average individual stellar masses are 1.09 M☉ and 0.90 M☉, respectively, though slightly higher masses have been quoted in recent years, such as 1.14 M☉ and 0.92 M☉, or totalling 2.06 M☉. Alpha Centauri A and B have absolute magnitudes of +4.38 and +5.71, respectively. Stellar evolution theory implies both stars are slightly older than the Sun at 5 to 6 billion years, as derived by both mass and their spectral characteristics."
 * This is repeating previously stated information and adds nothing to the discussion at this point. Is this a merge artifact?


 * Then we have a report from an apparent time-traveler:

"The closest approach in the future was in February 2016, at 4.0 arcsec through 300°."

Alpha Centauri A/B and Proxima Centauri are truly a bound system!
According to this source, Alpha Centauri A/B and Proxima Centauri are truly a bound system, with an orbital period of ~550,000 years. -- JP — Preceding unsigned comment added by 75.163.75.97 (talk) 21:18, 2 December 2016 (UTC)

Requested move 27 December 2016

 * The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review. No further edits should be made to this section. 

The result of the move request was: Not moved per WP:SNOW Fuortu (talk) 17:37, 27 December 2016 (UTC)

Alpha Centauri → Rigil Kentaurus – per International Astronomical Union, officially renaming it as Rigil Kentaurus, at https://www.iau.org/public/themes/naming_stars/ SkyFlubbler (talk) 07:53, 27 December 2016 (UTC)
 * Oppose. This is one of the best-known stars in the sky. The IAU announced this rename a month ago. We can wait to see if commonly consulted reference works follow suit or not. Pandas and people (talk) 08:55, 27 December 2016 (UTC)
 * Oppose. Rigil Kentaurus and Toliman have been old proper names for it anyway, so nothing has really changed. 99% of occurrences will still be for Alpha Centauri. Cas Liber (talk · contribs) 10:03, 27 December 2016 (UTC)
 * Oppose You have to be kidding? Alpha Centauri has to be by far the most common name. Fyunck(click) (talk)
 * Oppose per WP:Common name. — Huntster (t @ c) 10:31, 27 December 2016 (UTC)
 * Oppose per WP:COMMONNAME. Objects have multiple names, the Wikipedia uses the most commonly used as the article name. Tarl N.  ( discuss ) 12:44, 27 December 2016 (UTC)
 * Oppose because Alpha Centauri is one of the most commonly known stars in the sky and nobody is going to start referring to it as Rigil Kentaurus just because the IAU made it the offical technical name (WP:COMMONNAME) MarkiPoli (talk) 12:46, 27 December 2016 (UTC)


 * The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

Rigil Kentaurus in lead
The IAU list from the !vote above of course refers to "Rigil Kentaurus", but my interpretation of it suggests that this would only apply to a Cen A, not the whole system. Perhaps the Rigil Kentaurus reference should be moved to the second sentence and be parenthetical to a Cen A, just as Proxima Centauri is parenthetical to a Cen C, which would render the second sentence to read: "It consists of three stars: the pair Alpha Centauri A (also named Rigil Kentaurus) and Alpha Centauri B together with a small and faint red dwarf, Alpha Centauri C (also named Proxima Centauri), that may be gravitationally bound to the other two." Or, if the term should refer to the AB system, it could read "It consists of three stars: the pair Alpha Centauri A and Alpha Centauri B (together also named Rigil Kentaurus) together with a small and faint red dwarf, Alpha Centauri C (also named Proxima Centauri), that may be gravitationally bound to the other two." Thoughts? — Huntster (t @ c) 20:00, 27 December 2016 (UTC)
 * The name Rigil Kentaurus long precedes the knowledge that it was a double star, and as such has always referred to the AB pair (and I've seen references to Rigil Kentaurus A / Rigil Kentaurus B - for example, here, in an article about the renaming). Do we have evidence beyond a text file from someone's personal directory that the IAU intends the name to no longer refer to the pair of stars? It's possible they decided to do that, I haven't seen the minutes from the meetings. Tarl N.  ( discuss ) 21:33, 27 December 2016 (UTC)
 * It refers to Alpha Centauri A, not the AB pair. I will go ahead and WP:BOLDLY make the appropriate changes to the article. —MartinZ02 (talk) 00:40, 28 December 2016 (UTC)


 * Why did the IAU do the rename? "The move was intended to reduce confusion, according to the IAU." If that's the actual reason, I'd say they need to rethink this issue. Pandas and people (talk) 15:48, 29 December 2016 (UTC)
 * I am cynical about it. Most of the ones in use are standardized anyway (e.g. you very rarely see any spelling other than "Betelgeuse" these days). If anything, the ones I think they should have prioritized on were brighter stars that lacked Bayer or Flamsteed designations and as those damn HD and HIP numbers are impossible to memorise! Cas Liber (talk · contribs) 21:29, 30 December 2016 (UTC)

Twin stars with different ages?
What we have is completely stupid. They have to be the same age, but the entry says otherwise. And contradicts what the aricle says: it clearly gives a range. --GwydionM (talk) 16:09, 30 December 2016 (UTC)

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Alpha Centauri Bb & Bc
The reference and statement that a possible other planet was found in 2013 is inaccurate. The reference actually refers to the planet described in the next section ("Possible detection of another planet"), which bears the correct reference. This statement about another planet should thus be deleted in "Alpha Centauri Bb & Bc" and the section renamed "Alpha Centauri Bb", and the next one "Alpha Centauri Bc" Pcauchy (talk) 10:35, 9 April 2018 (UTC)

Johnson vs Henderson?
I just popped in to enquire about an internal conflict in the text regarding the history. I see there's been a lot of traffic about some math issues here, I hope my entry doesn't get lost...

Anyway: in the Observational History section we read that Manuel John Johnson writes to Thomas Henderson about having observed a high rate of proper motion for alpha Centauri, and Henderson investigates and subsequently measures a large parallax. But down in the Kinematics section, we read that Thomas Henderson discovered "the true distance" to alpha Centauri, by a means not stated, and went on to investigate if it might have a large proper motion, by looking back to position measurements taken 80 years earlier. Mr Johson is excluded from this version of the events.

So, what gives? Is this simple oversight, or are their competing claims lurking behind this? Can we arrive at a single narrative? 173.180.151.52 (talk) 08:22, 11 April 2018 (UTC)just some curious wiki reader...
 * It's not really for us to arrive at a single narrative. The claim that Johnson determined the proper motion and informed Henderson comes from a biography of Johnson written in 1982. That may or may not be accurate - biographies written long after the fact sometimes distort actions and timelines. On the other hand, it would have been impossible for Henderson to measure the parallax without also measuring the proper motion, but he didn't publish until later. Johnson may well have published the proper motion before Henderson published parallax, but I don't see a citation to that effect. Given the fuzzy timeline through the 1830s, it may not be possible to clear this up. Tarl N. ( discuss ) 18:03, 11 April 2018 (UTC)

Deleted unsubstantiated table of planets
Since the data in the table of planets is contradicted by the subsequent paragraphs, and it is the text rather than the table that is ref'd, I deleted the table. I haven't checked the refs to verify the text either, though. — kwami (talk) 06:04, 19 April 2018 (UTC)

Apparent magnitude of components....does anyone care if Alpha Centauri A is fainter than Arcturus?
The material in question is this. Anyone else keen on opining on keeping vs removing it? Cas Liber (talk · contribs) 01:27, 24 June 2018 (UTC)


 * The discussion is in the Archive 1 "Arcturus"


 * At −0.27v visual magnitude,[11] Alpha Centauri appears to the naked-eye as a single star and is fainter than Sirius and Canopus.
 * I have reverted an erroneous edit of this sentence. The editor was not reading it carefully enough. It is discussing the combined appearance of α Cen A and α Cen B. He changed it to the incorrect:
 * At −0.27v visual magnitude,[11] Alpha Centauri appears to the naked-eye as a single star and is fainter than Sirius, Canopus and Arcturus.
 * At -0.27, the combined light from Alpha Centauri does make it brighter than Arcturus at -0.05. It is α Cen A alone, at +0.01 which is fainter than Arcturus, as the very next sentence points out.
 * The original sentence had it right. B00P (talk) 11:12, 5 March 2009 (UTC)


 * Also other discussions are here Arianewiki1 (talk) 06:35, 24 June 2018 (UTC)

Group of physicists would like to help update Alpha centauri
Hi! A set of astronomers and physicists have offered to help update the Alpha centauri article. Some got together and discussed this at the EWASS2018 conference, and the others are from NASA Ames. Would you be interested in being involved? After the update, I'm also encouraging them to submit it for both GA review, and for external academic review by WikiJSci. I'll make a post on the Alpha centauri talk page so that there's a record there too. None have previously edited Wikipedia (to my knowledge), so I'll watch the page to help out with formatting, and I've pinged, , and. T.Shafee(Evo &#38; Evo)talk 04:20, 20 June 2018 (UTC)
 * I am happy to help with formatting etc. I have experience with Good and Featured Articles. Cas Liber (talk · contribs) 04:37, 20 June 2018 (UTC)
 * As long as they can source whatever they change, anyone can edit the article. But it can't just come from their heads. The info needs to have been published somewhere. Fyunck(click) (talk) 05:15, 20 June 2018 (UTC)
 * Fully agree - I'll prep them on WP:Verifiability so that there's an understating of what's expected in terms of referencing. T.Shafee(Evo &#38; Evo)talk 06:26, 20 June 2018 (UTC)
 * I will be willing to help with formatting, but I have very limited knowledge in the field of astronomy of GAs, so that's why it was a foolish for me to GAN this article. <b style="color:#060">L293D</b> (<b style="color:#000">☎</b> • <b style="color:#000">✎</b>) 12:07, 20 June 2018 (UTC)
 * Just FYI and to help! I reviewed Alpha Centauri here which includes what's left from GA1 review and some recent work on Alpha Centauri B. --Marshallsumter (talk) 04:08, 21 June 2018 (UTC)
 * is your group of scientists planning to register accounts? <b style="color:#060">L293D</b> (<b style="color:#000">☎</b> • <b style="color:#000">✎</b>) 19:04, 25 June 2018 (UTC)
 * I recommended that as the first step. I suspect they will take a little while to organise themselves, so I'll ping back here when I next hear from them. T.Shafee(Evo &#38; Evo)talk 23:31, 25 June 2018 (UTC)

Additions of lux units
An anonymous IP (with an ever-changing IP address, so I can't use their talk page) has been adding text to describe magnitudes in units of lux, a unit primarily used in photography. I find the additions to be largely noise (this is an astronomy article, not a photography article), and would like to remove them. They aren't cited, and the IP claims they are "routine calculations". If they are that routine, they don't need to be in this article. Does anyone particularly like the additions? <b style="color:green">Tarl N.</b> ( discuss ) 03:02, 3 July 2018 (UTC)
 * No, agree on their removal. Cas Liber (talk · contribs) 20:42, 3 July 2018 (UTC)
 * I also agree that they should be removed. Attic Salt (talk) 20:48, 3 July 2018 (UTC)
 * Done. I think that entire section (From a hypothetical A or B planet) needs to be redone with proper citations. <b style="color:green">Tarl N.</b> ( discuss ) 20:55, 3 July 2018 (UTC)

Motion of Alpha Centauri
Years ago you edited this article, adding paragraphs about its proper motion. But I don't think it's correct. The page now says (up in the box) that α Centauri B has a different proper motion from that of α Centauri A, which is the proper motion that you used. This is obviously because they orbit one another, so they are movin' with respect to their centre of mass. What's important for the long term is the motion of the centre of mass, which is easy to calculate if we know their masses accurately. Since their masses are similar, the centre of mass will have a proper motion right about the average of the two. So that means it's not movin' the way you describe. Eric Kvaalen (talk) 07:28, 24 December 2017 (UTC)
 * Agreed. The HIP proper motion was determined individually for both stars. However, it is not necessarily half the mean motion nor its centre of mass. Motions were set at the epoch of 1991.25. Kervella et al., A&A, 594, A107 (2016), gives the true proper motion of both stars as pmRA=-3619.9, pmDec=+693.8 Epoch 2000.0 or cpm.=3685.79 mas (Half of the HIP2 data is -3646.82, +638.28, cpm=3702.26mas.) Using the α Centauri A data in text, gives cpm.=3709.4 mas., or merely 0.2% in error.
 * All examples are essentially true (but not exact), however, the more northerly motion calculates only a little higher. I.e. In PA 280.9° instead if just using α Cen A motion PA 277.5°. Worst as the given proper motions are not constant, and are actually slowly accelerating in respect of the Sun, due to the stars own true motion in approach us. In about 40,000 years they will reach a maximum proper motion before instead reducing.
 * Considering all the errors, these calculations are good enough to extrapolate for about 10,000 years. Including the no research policy, etc., the results are good enough I'd think. Thanks. Arianewiki1 (talk) 03:35, 25 December 2017 (UTC)


 * You gave, for the RA and Declination proper motions in milli arc seconds per year
 * -3678 481.84
 * According to the article now, the values for star A and star B are:
 * −3679.25 473.67 for α Cen A
 * −3614.39 802.98 for α Cen B
 * Using masses of 1.100 and 0.907 respectively gives, for the centre of mass:
 * -3649.93 622.49
 * So your value for the proper motion in RA is less than 1% off, but your value for proper motion in declination is off by a huge amount. In other words the system is movin' north much faster than what you wrote. I think the image is wrong too (though it wasn't you who put it in). The westward movement should be about six times as much as the northern movement. So it won't go that close to β Centauri.
 * Eric Kvaalen (talk) 07:25, 25 December 2017 (UTC)
 * Please explain how you are getting centre of mass pm. of -3649.93, +622.49. [Here, you'll also need to calculate knowing the epoch, spectroscopic orbit and parallax; and you need to know the date of the true orbit nodes when the stars travel in parallel motion. It is not simple to do. Knowing the masses alone gives a wrong result.] Certainly, the barycentric motion pm. value must be about -3619.9±3.9 +693.8±3.9 mas. (2000) (You must assume this is correct because it is able to be formally cited.) Also β Cen is 27′ 39.44″ further south north than α Cen (2000).
 * No, α is that much further south. Eric Kvaalen (talk) 14:21, 30 December 2017 (UTC)
 * α Cen 14h 39m 36.49s -60° 50′ 02.37″ (2000)
 * β Cen 14h 03m 49.41s -60° 22′ 22.93″ (2000) Separation is 4.38° (2000)
 * To calculate approximate positions in past or future add pm. -3619.9, +693.8 arcsec per century (cpm.=3673.0 mas.) for α Cen and pm. -33.3, -23.1 arcsec per century (cpm.=40.53 mas.) for β Cen. (β Cen rather trivial)
 * Calculations using these updated motions finds closest approach is now:
 * Using citable pm. -3619.9±3.9 +693.8±3.9 in 6381.5±0.4 AD with closest approach 0.40° or 24.0′ north of β Cen.
 * Changing to your -3649.93 622.49 gives 6340 AD 0.31° or 18.4′N.
 * Using -3678, 481.84 is 6306AD 0.13° or 7.9′N.
 * Or the old Hartung reference using -3606, +705 mas finds 6385.5AD at 0.41° or 24.9′N. (Published as 23′N in 5973AD and in his 1968 edition 23′N in 6200AD.)


 * So date certain at 6380±20AD, with distance 0.4°±0.1° or 24′±5′ North.


 * Note: If you do use Stellarium, this motion is wrongly displayed, and is a known error that isn't fixed as yet. Arianewiki1 (talk) 05:23, 26 December 2017 (UTC)


 * Well, I don't understand what you mean about spectroscopic orbit and all that, but you seem to be agreeing with me that what the article now says is wrong. When you say that the values are about -3619.9±3.9 +693.8±3.9 mas/y and that this can be formally cited, what do you mean? What is the source? Let's use that and give the source! By the way, what is Stellarium? Eric Kvaalen (talk) 07:08, 26 December 2017 (UTC)


 * I've just edited the article, improving some of your changes. If there is something you disagree with, I can explain. The human eye can distinguish things separated by 60 arc seconds – it's part of the test for 20/20 vision (see Angular diameter).


 * I was wonderin', where did you get the figure of 53° S which you put for the declination back in the time of Ptolemy?


 * Please respond to my questions of yesterday as well!
 * Eric Kvaalen (talk) 07:51, 27 December 2017 (UTC)


 * The spectroscopic orbit is based on the variable radial velocities, and you need to know the time when both the stars are traveling the same direction. Also the stars in Alpha Centauri's case are close to us and currently approaching, the mean radial velocity of system needs to be known to the calculate how the proper motions change. I.e. v= 4.74 ( d (pc) x cpm (arcsec/yr) )
 * The reference (already mentioned above) is Kervella, et al., A&A, 594, A107 (2016) "Close stellar conjunctions of Centauri A and B until 2050" pg.4-5
 * You say "...you seem to be agreeing with me that what the article now says is wrong." The article is based on the best data available, and if you read it, it never too specific because depending how the calculations are done, there is some error in the given result. (Just see my examples above!)
 * This book "Alpha Centauri: Unveiling the Secrets of Our Nearest Stellar Neighbor" by Martin Beech pg.16 shows the path travelling near Beta Centauri
 * What is Stellarium? It is a free planetarium/sky atlas.[www.stellarium.org] This can do the precession for you, by just setting the date. aka. c. 58 53 degrees. (Easily calculated too.) I.e. 141 AD, (Also Ptolomy Centaurus stars are also significantly out because no atmospheric refraction wasn't taken into account.)
 * As for "The human eye can distinguish things separated by 60 arc seconds – it's part of the test for 20/20 vision (see Angular diameter)." Not possible and is unreliable. Too many variables with starlight for it to be reliable. Arianewiki1 (talk) 12:34, 28 December 2017 (UTC)


 * Ah, I didn't notice that you were usin' the same number as you had referenced earlier. e.g. P. Kervella et al.. "Close stellar conjunctions of α Centauri A and B until 2050 (2016 ) Thanks.
 * As I said before, the article uses a value for the northward motion which is like 50% too low – 418.84 instead of 693.8, and so it predicts an approach to β Centauri which is much too close. I'll change it.
 * Is there an on-line "planetarium" or something, which can tell us the declination in Ptolemy's time? I calculated 51° S, but you say 53°. If we had an on-line source we could cite it. (I don't understand what you meant by "aka. c.58 degrees".)
 * I just did a test with two flashlights and one wife, and she couldn't tell that there were two flashlights when they were only 60' apart. So maybe you're right. But at the moment there is a reference to the statement about 60'.
 * Eric Kvaalen (talk) 12:20, 30 December 2017 (UTC)

Really. Enough already. I'm getting pretty tired of you making wild unsubstantiated statements and claims without any proof. e.g. Values for proper motion that you calculated nor 418.84 is 50% of 693.8, etc. (It is the difference between the common proper motions that are important NOT the individual motions. The significant pm in RA makes the pm in declination fairly minor.) Yet another is your statement "What's important for the long term is the motion of the centre of mass, which is easy to calculate if we know their masses accurately." As shown, it is neither easy to obtain and relies on many other assumptions.

Again you seemingly have little to no comprehension of the difficulties nor the errors involved here, and your last article editing attempt readily shows this - especially when the error is already about 5 to 10 arcmins. I state "So date certain at 6380±20AD, with distance 0.4°±0.1° or 24′±5′ North". Instead you just ignore it, and continue rabbiting on about some imaginary mistake and point-blank refuse to listen.

Worst now in your latest edit, even Kervalla does say what you say and it does and does not give any long term predictions beyond 2050.

So when you say your initial post :"So that means it's not movin' the way you describe." is plainly false and uttely wrong!!

You openly stated: "The page now says (up in the box) that α Centauri B has a diffhave erent properd motion from that of α Centauri A, which is the proper motion that you used." But I never used the A star to calculate the proper motion to find the nearest approach to Beta Centauri. All I did was state: the motion was "I.e. About 6.1 arcmin/century (367.8 arcsec/ century) equivalent to 1.02 degrees/millennia or 61.3 arcmin/millennia." The difference between either component cpm, is not significantly different to the precision stated. I.e. It is not actually/necessarily "wrong" (but you continue to say it is.) Also in 2008, I only said :"A simple rough calculation, for example, show that the current distance of 4.4° etween Alpha and Beta Centauri will take about 4200 years by proper motion to cross, or about A.D. 6200. Calculating backwards in time, say to the time of 2000 years ago, the pointers of Alpha and Beta Centauri were about 6½ degrees apart when Alpha Centauri was instead lying in the present day constellation of Circinus." I never stated a observed distance in 6200 AD between Alpha and Beta at all. Yet even in the next section, I gave the earlier reference Hartung (1994), which has since, been removed, that the stars will pass by 23 arcmin. This now has been readded.

As for removing Matthew's reference why do it? nd they change as the distance, and Matthew's shows how it is calculated. (In 2008, I even said "A more precise calculation can be made that involves taking into account the slight changes in the distance of the star by its own motion, and in Alpha Centauri's case, this means a slow increase in the values of these proper motions. Slight variances are also due to the small difference in measured values of the proper motions of Cen A and Cen B, which are about 0.5%."! Matthew's is also the basis of the figure explaining the distances of the nearest stars over 100,000 years.

Lastly making an edit then saying "Took out a couple things which I will discuss on the Talk page." in unacceptable editing. If you do make edits, discuss it on the talkpage first if you are unsure if the content and get the necessary consensus.

So far you have shown little proof towards many of your contentious statements and have likely just simply relied on me to do the 'heavy lifting.' Talkpages are for discussing things to reach consensus. It is not made available here as a tool to teach others about the intricacies of the subject nor their gaps in their knowledge.
 * Note 1: If you must add the information of Kervalla (2016), then add it to the Star Box, under 'Astrometry', addding the system as 'AB' You should probably also add this to the Distance table at the bottom of the article. Adding new figures intoo the document just confuses things IMO, and then you have to justify it.


 * Note 2: I've corrected the two mistakes in my replies above. Arianewiki1 (talk) 04:36, 31 December 2017 (UTC)

You didn't give me a chance to explain before reverting my edit. I'm in France and I think you're in Australia. I finished my edit and went to bed.

So let me explain everything I did.

When I said that the proper motion in the northerly direction was off by 50%, it was an approximation. I chopped off the digits after the first, so I was comparing 600 and 400. 600 is 50% greater than 400. What difference does it make if the error was actually only 40% or 30%? The point is it was way off. I still think that the proper motion of the centre of mass is easy to calculate from the proper motions of the two stars if we know their masses, but never mind! I took your value instead! (That is, the value you mentioned here, from Kervella 2016.) You say you never used the A star to calculate the proper motion to find the nearest approach to Beta Centauri. But you did give the A star proper motion in the paragraph which was talking about the motion of α Centauri as a whole. (You gave, and you have now restored, the value of 481.84, which is apparently a version of the number which we now give as 473.67 for α Cen A.)

As for whether it's important whether it's 481 or 694, it makes a difference in how close it will get to β Centauri. Somebody made a picture showing how α Centauri moves to be very close to β Centauri. Yesterday I made a graph in Excel to see whether his picture was correct. I can send you the Excel file if you want. My graph shows that it doesn't get as close as in his picture. So I took out his picture. I don't know where he got his data, but it may be that he was using your number (481) instead of the correct number, 694.

I don't know what you mean above when you say "especially when the error is already about 5 to 10 arcmins".

When you say I ignore your statement "So date certain at 6380±20AD, with distance 0.4°±0.1° or 24′±5′ North" I don't know what you want. Do you want me to put that into the article?? Actually, in my Excel calculation it comes out about 0.7° north of β. I don't know how you did your calculation. So I didn't put in any number. All I did was to change the sentence at the end of the section where it said that "In about 4000 years" α will be close to β, to say "Around 6300 AD". Isn't that better? (Again, my Excel calculation finds that the closest approach is around 6300, not 6380. But that's not important, and I didn't say "exactly 6300".)

What do you mean when you say "Worst now in your latest edit, even Kervalla does say what you say and it does and does not give any long term predictions beyond 2050"? Kervella certainly does give the numbers I wrote where I cite him. I did not say anything about him making predictions beyond 2050! Why have you now put back the incorrect numbers?

I don't understand what you want when you say, "I never stated a observed distance in 6200 AD between Alpha and Beta at all." What does that have to do with me or my edit?

As for the references to Matthews, I glanced over the paper and I couldn't see anything that supported any of the statements where he was being referenced, except I suppose the sentence "The Alpha Centauri system will then begin to move away from the Solar System, showing a positive radial velocity". But that doesn't need a reference. I did put the reference in, at an earlier spot, just so it would still be in the list of references, but I had a hard time deciding where to put it because it's not really needed anywhere.

Getting back to the other changes I made, I put in the other velocity components (westward and northward).

I put in a great animation which I found on the Italian article.

I put in the very interesting fact that the stars of Alpha Centauri are going to pass in front of several other stars in the next few decades, including one where it might make an Einstein ring.

I improved the English in the paragraph about Alpha Centauri's approach toward us.

I restored the words "by equations" which you had written and someone else had deleted. I wanted to ask you (when I got around to the Talk page as promised) what you meant by the sentence, "Consequently, the observed position angle of the stars are subject to changes in the orbital elements over time, as first determined by equations of W. H. van den Bos in 1926."

I took out the sentence "Some slight differences of about 0.5 percent in the measured proper motions are caused by Alpha Centauri AB's orbital motion." It seems to be wrong. Look at the graphs in Kervella 2016. You can see that the motions of A and B are not withing half a percent one of the other!

I took out the picture of Alpha approaching Beta (as I mentioned above), and I moved the graph of the closest stars up to the place where it's relevant.

I improved the English of the paragraph about when Alpha Centauri gets close to us.

I took out the text, "somewhere in the faint present day southern constellation of Telescopium. This unusual location results from the fact that Alpha Centauri's orbit around the galactic centre is highly tilted with respect to the plane of the Milky Way." It had a reference to Matthews, but I don't see anything in Matthews that supports it. Right now, Alpha Centauri is moving more or less straight west, which is the direction that the Milky Way goes in that part of the sky. And it doesn't make any sense that it will end up in Telescopium. That is almost a full circle away from where it is now. It can only make half a circle around us (unless it is severely deflected by the gravitational pull of the sun). And it has already made a good portion of that half circle, so it will move less than 180° in the future.

I also wanted to ask you what you meant in your footnote that says, "Calculated as; θ − θo = μα × sin α × (t − to ), where; α = right ascension (in degrees), μα is the common proper motion (cpm.) expressed in degrees, and θ and θo are the current position angle and calculated position angle at the different epochs."

And again I ask, is there an on-line "planetarium" or something, which can tell us the declination in Ptolemy's time? I calculated 51° S, but you say 53°. If we had an on-line source we could cite it.

Eric Kvaalen (talk) 08:05, 31 December 2017 (UTC)

This morning I decided to see whether I could read the Hartung reference, since it seems wrong to me. I found that I could read the relevant passage in Google Books: Centaurus (Cen)

Centaurus, the centaur, is a very large southern constellation included in Ptolemy's Almagest of AD 150, and he assigned thirty-seven stars to it. Apart from Orion, it is the only constellation to have two first magnitude stars, the well-known Pointers to the Southern Cross. Today, they can hardly be seen above the horizon in latitude 30 degrees north, but 2000 years ago they were about 10 degrees farther from the celestial pole. Centaurus is in fact a very ancient group and to the Greeks appears to have typified the wise and benevolent Chiron in contrast to the wild predaceous centaurs represented by Sagittarius. The area is 1060 square degrees and the centre culminates at midnight about 6 April.''

''The two bright stars α and β Cen, do not point at present directly to Crux but somewhat north of it. However, owing to the proper motion of α, this direction is slowly swinging southwards and about AD 4000 will indicate the centre of the cross when the separation between the stars will be little more than half of the present 4.5°. Closest approach will occur about AD 6200, α Cen being then some 23' north, and the pair will form a conspicuous and brilliant object in the southerm sky. Such a conjunction between two first magnitude stars will not occur again for an immense interval of time."'' [From page 194] Unfortunately this doesn't give any reference for the 23' nor any indication of the basis of the calculation. It does though support my contention that the declination 2000 years ago was 10 degrees further north than now, that is −51 degrees rather than your −53.

Eric Kvaalen (talk) 07:05, 1 January 2018 (UTC)
 * Hartung's is the reference. It's generally considered a WP:RS, and as such, facts may be extracted and put into Wikipedia. We do not require reliable sources to document every assertion they make, although that can come into play when multiple sources present contradictory statements. Tarl N.  ( discuss ) 22:56, 1 January 2018 (UTC)


 * Again. Please Eric Kvaalen stop making multiple false statements. e.g.
 * "This morning I decided to see whether I could read the Hartung reference, since it seems wrong to me." How can any published cited source be wrong here? (especially where it is independently and demonstrated as verifiable!)
 * Another is "I also wanted to ask you what you meant in your footnote that says, "Calculated as; ..." This is not my footnote, and it is not even relevant to the common proper motion of the star.
 * As for "I took out the sentence "Some slight differences of about 0.5 percent in the measured proper motions are caused by Alpha Centauri AB's orbital motion." It seems to be wrong. Look at the graphs in Kervella 2016. You can see that the motions of A and B are not withing half a percent one of the other!" This just shows gross evidence of utter incompetence. Some of the error is taking about the differences in the cpm is also caused by the errors with the orbital motion of the binary star. e.g. The HIP2 error is pm of A=−3679.25±3.86 (0.10%) B=-3614.39±20.42 (0.56%) ΣAB error is -3646.82±20.78 (or 0.48%). Error therefore is about 0.5% and the statement is justified.
 * SIMBAD states here the pm is -3608±30 and 686±25 mas.yr -1 (oddly not cited), which makes the cpm. -3663.6±39 or 1.06%.
 * As for "And again I ask, is there an on-line "planetarium" or something, which can tell us the declination in Ptolemy's time? I calculated 51° S, but you say 53°."
 * Why is this even relevant? Show me the calculation you use here, because it must be in error? On what basis are you actually using Ptolemy's position here? (There are three possible data sources, actually.)
 * Now. If you use 'Stellarium' in Epoch 150AD is λ=216° 21′ β=-43° 25′ (λ=239° 27′ β=-42° 35′ (2000)) Ptolemy gives for Star 969: λ=215° 20′ β=-41° 10′ (150AD) - a significant error. Just using precession + cpm. for true current position α Centauri finds the position as α=12h 45m 47s δ=-53° 21′ 06″ (150AD) from 14h 50m 30s -62 -60° 27′ 45″ (2000) Using the 'Ptolemy' software available here  confirms this too. Therefore, declination of -53°S is completely valid.
 * It is clear to me you have very poor concepts regarding errors nor in applying them when applied understanding the significance of some quoted value. e.g. Persistently saying things like "'I don't know where he got his data, but it may be that he was using your number (481) instead of the correct number, 694."
 * Again. [IT IS NOT MY NUMBER] It matters not at all. I just expressed that : "...the average cumulative common proper motion (cpm.) of Alpha Centauri AB is about 6.1 arcmin each century, and 61.3 arcmin or 1.02° each millennium." e.g. Common proper motion being  cpm=sqrt(pmRA^2+pmDec^2). There is absolutely no stated vector / position angle here.


 * PROOF
 * A=−3679.25 473.67 cpm.= −3709.62 mas.yr=1
 * B= −3614.39 802.98 cpm.= −3702.51 mas.yr=1
 * Average is: -3706.05±0.58 3σ Error is trivial!!
 * Simple calculation:
 * Using mean 3.70605 arcsec×100 = 370.605 arcsec = 6.18 arcmin / yr = 61.8 arcmin / 1000 years = 1.03°/1000 years
 * Using HIP (not HIP2) value of -3679.25, 481.84 in pmDec for 'A' finds cpm.=-3647.67, hence:
 * -3647.67 arcsec×100 = 364.767 arcsec = 6.07 arcmin / yr = 61.8 60.7 arcmin / 1000 years = 1.01°/1000 years
 * Difference is therefore trivial.
 * Rough average (as per document) is about "...6.1 arcmin each century, and 61.3 arcmin or 1.02° each millennium."


 * For the last time. Again, the values of the proper motion is distance dependent, and they are also are changing in magnitude overtime, hence require an Epoch (2000). The values will be different in epoch 6300AD than now, which is all explained by Matthews (1994).


 * As for saying. "When you say I ignore your statement "So date certain at 6380±20AD, with distance 0.4°±0.1° or 24′±5′ North" I don't know what you want. Do you want me to put that into the article?? Actually, in my Excel calculation it comes out about 0.7° north of β." Clear your calculations are plainly wrong. (Did you account for Beta Centauri's motion, obliquity, change in proper motions via: v= 4.74 × d (pc) × cpm (arcsec/yr)?) Explaining it. Well that not my problem. I have given you a formal cite, stating 23′ (now in the article) being Hartung (1994). I have given another (linked) reference that agrees with this: ""Alpha Centauri: Unveiling the Secrets of Our Nearest Stellar Neighbor" by Martin Beech pg.16 shows the path travelling near Beta Centauri ."


 * Frankly, its your own competency that I question.
 * I'll waste no more time on this. Arianewiki1 (talk) 04:41, 2 January 2018 (UTC)


 * Just noticed you said: "It does though support my contention that the declination 2000 years ago was 10 degrees further north than now, that is −51 degrees rather than your −53." Rubbish. Let's see.
 * As said above: "α Centauri finds the position as α=12h 45m 47s δ=-53° 21′ 06″ (150AD) from 14h 50m 30s -62 -60° 27′ 45″ (2000)", which is a difference of 09 07° 08′ 36″. (Using -51° by the way is 11° 08′ 36″)
 * By using given pmDec=693.8 by Kervella et al. (2016), gives the total between 2000-150=1850 years, meaning 1850×0.6938 arcsec/60/60=0.3565° or 21′ 23.5″. Adding this to δ=-53° 21′ 06″ (150AD) is actually -53° 42′ 32″. (Alpha Centauri in the past was (relatively) once further south.)
 * Difference of 09 07° 08′ 36″+21′ 23.5″ now becomes 09 07° 30′ 00″ or 9 7½°. Closer to Hartung estimate of 10°, eh?
 * So does this now validates your -51° contention? It doesn't. Arianewiki1 (talk) 05:39, 2 January 2018 (UTC)


 * You said "It does though support my contention that the declination 2000 years ago was 10 degrees further north than now," Hartung actually says α and β Centauri was "...but 2000 years ago they were about 10 degrees farther from the celestial pole." Let's again see. So the calculation above becomes;
 * δ=-52° 40′ 44″ (1AD) diff =09° 47′ 01″ +cpm. 2000×0.6938 arcsec/60/60=0.38524° or 23′ 08″ =10° 10′ 09″ or 10.2°.
 * But actually, Ptolemy placement was in about 150AD, making the value 09° 30′ 00″ or 9½°. If now the position is 14h 50m 30s -62 -60° 27′ 45″ (2000), then Declination was -62° 27′ 45″ + 09° 30′ 00″ is about -53°S NOT -51°. Arianewiki1 (talk) 06:33, 2 January 2018 (UTC)

Yes, I realize that we don't require a reference to give other references or document every statement. But on the other hand, if we are convinced that a statement in a reference is wrong, then we can take it out. Obviously that requires consensus. It's an easy calculation to make though.

Of course published cited sources can be wrong! I don't know what you mean by "independently and demonstrated as verifiable". As I said to Tarl, it's an easy calculation to do. All we need are the proper motions of α and β and their present positions.

The footnote that starts "Calculated as" you added in 2008. I never said it was relevant to the common proper motion of the star. But I still want to know whta you meant.

Concerning the sentence "Some slight differences of about 0.5 percent in the measured proper motions are caused by Alpha Centauri AB's orbital motion", it sounds to me (this is how I understood it) to be saying that the differences between the proper motions of A and B are only about 0.5 percent. But the ratio using the number you give is 3679.25/3614.39 or 1.018, a difference of 1.8%. Of course, this varies with time. Did you take a look at Figure 1 of Kervella? Or look at.

We see here that in the five years following periapsis B moves about 4" westward and 10" southward compared to A. Since they have approximately equal masses, that means B moves on average about 0.4" westward and 1" southward per year compared to the barycentre, and A moves 0.4" eastward and 1" northward per year. Compare that to the generally westward motion of the barycentre at 3.7" per year, and you can see that in that period the annual proper motions of A and B are very different – about 4" W and 0.3" S for B and 3.3" W and 1.7" N for A. You can see this in Kervella's Figure 1 around the year 2040.

You ask why it's relevant what the declination was in Ptolemy's time. Because I want to put the number into the text! I see now why my calculation was off. I didn't include the proper motion over the last 1900 years. I used 212° 27' for λ and −42° 35' for β. The proper motion has moved it toward the ecliptic by about a degree, and the 4° change in β moved it north by more than a degree because the circles of constant β do not coincide with the circles of constant declination. I would still like a reference or an on-line site that we could use in order to give the declination in Ptolemy's time.

I never said that you stated a "vector / position angle". What I said is that you gave (and have now restored) the northward proper motion as 481 mas/y when it should be 694 mas/y. That's not a trivial error. As I have said, it makes a difference in how close it will get to β Centauri. But why do you insist on giving values for A instead of for AB? As I have said in the paragraph before last, the proper motions of A and B individually vary a lot over the 80-year period. What we should give is the common proper motion. By the way, the common proper motion is not the length of the vector of proper motion as you say, it is the vector of proper motion which is common to two or more objects.

Of course the proper motion will be slightly different in 6300 AD. I never said anything about that.

Why do you say that my calculation of the closest approach to β Centauri is clearly wrong? You haven't seen it.

The proper motion of β Centauri is less than 40 mas/y in each direction, which comes to 160" (less than 3') over 4000 years. I don't know what you mean when you ask whether I account for obliquity, or change in proper motion. What I have done is simply to extrapolate what happens if the system moves 3.62" west and 0.694" north per year, with β Centauri sitting 4.4° west and 0.16° north of the present position. If you want, I can do a calculation in which the system moves along a straight line with a constant speed, presently described as 22.9666 km/s west, 4.4019 km/s north, and 22.3930 km/s towards us. I don't think that will change the result much!

I don't know where you got a declination of 62° 27' 45" S. I agree now that the declination in Ptolemy's time was about 53° S (see above). But now you're calling what Hartung said "rubbish"! Yet you claim that his statement "in AD 6200, α Cen being then some 23' north" is sacrosanct!

You didn't address many of the things I said on December 31.

Eric Kvaalen (talk) 13:12, 2 January 2018 (UTC)
 * You need to be more concise about precisely what you need answers to. See WP:WALLOFTEXT.
 * As a general comment on the issue of position, when you object to a published source's assertion, you need to either find another published source which contradicts it, or demonstrate that it is wrong and remove the assertion.
 * Note, if it's your own calculations, you can't replace a published source's assertion with your own; that would be WP:OR. Publishing a value contrary to an existing source should be done by conventional means, in a conventional WP:RS where you have to get through an editorial board and preferably peer review. Once it's published there, someone (preferably not you) can pick up the revised statement and add it to Wiki.
 * Yes, that's complicated. But Wikipedia is NOT a venue for publishing new conclusions. Tarl N.  ( discuss ) 18:13, 2 January 2018 (UTC)

For once I'll be brief. Eric Kvaalen said "As I said to Tarl, it's an easy calculation to do. All we need are the proper motions of α and β and their present positions." This plainly shows you are missing the whole point. It is actually far from 'easy' to do, especially as the values quoted have considerable errors. I've explained this now a dozen times. Furthermore, your latest response contains so many terrible flaws and mistaken ideas, that it is next to impossible to answer. e.g. The orbit of α Centauri is actually mostly independent from the common proper motion.

As for "What I said is that you gave (and have now restored) the northward proper motion as 481 mas/y when it should be 694 mas/y. That's not a trivial error. " Yet more importantly the cpm only differs by just 7.11 mas.yr=1 I.e. From A=−3679.25 473.67 cpm.= −3709.62 mas.yr=1, B= −3614.39 802.98 cpm.= −3702.51 mas.yr=1. (I actually now have removed these 'disputed' values from the article, because they are unnecessary.) Using either doesn't change the cpm. by very much hence: "...the average cumulative common proper motion (cpm.) of Alpha Centauri AB is about 6.1 arcmin each century, and 61.3 arcmin or 1.02° each millennium." Is this statement true.

Finally. In saying "You didn't address many of the things I said on December 31." is just insulting. I reverted your edits because they were just wrong or had false statements. Worst. In removing the cite by Matthews (1994) was unjustified and simply showed your own very poor understanding of the problem. e.g. Your own words (again) "As I said to Tarl, it's an easy calculation to do. All we need are the proper motions of α and β and their present positions."

''Toutes les fautes sont à vous. Clairement. Pensée sans sagesse.'' Merci. Arianewiki1 (talk) 01:24, 3 January 2018 (UTC)


 * ===Problem Has Been Solved===
 * Eric Kvaalen said "What I said is that you gave (and have now restored) the northward proper motion as 481 mas/y when it should be 694 mas/y. That's not a trivial error. As I have said, it makes a difference in how close it will get to β Centauri. But why do you insist on giving values for A instead of for AB? As I have said in the paragraph before last, the proper motions of A and B individually vary a lot over the 80-year period. What we should give is the common proper motion. By the way, the common proper motion is not the length of the vector of proper motion as you say, it is the vector of proper motion which is common to two or more objects."
 * The article now says: "Combining the 2007 revised data from the Hipparcos Star Catalogue (HIP) for the main binary star components[84][85], the average cumulative common proper motion (cpm.) of Alpha Centauri AB is about 6.1 arcmin each century, and 61.3 arcmin or 1.02° each millennium. These motions are about one-fifth and twice, respectively, the diameter of the full Moon. Using spectroscopy the mean radial velocity has been determined to be around 20 km/s towards the Solar System."
 * I stated the main reason for this edit as: "Fixed cpm issues, removed statements/data that could be misinterpreted " Hence, this question has now been resolved. Eric Kvaalen either challenge these values of 6.1, 61.3 or 1.02° or the given cites. If not, drop it, and please don't mention this topic aspect again. Thanks. Arianewiki1 (talk) 01:56, 3 January 2018 (UTC)

Tarl, I am well aware of the rules of Wikipedia. But as you say, if we demonstrate that a published statement is wrong, we can remove it.

You say I should be more concise about what I need answers to. Basically, User:Arianewiki1 reverted my latest edit, and I wrote a long defense covering everything I had done in that edit. He has not answered most of it, and I contest what he has answered (mostly). So here is a list: This morning he removed the statement "Some slight differences of about 0.5 percent in the measured proper motions are caused by Alpha Centauri AB's orbital motion". So I guess he know agrees that that was wrong.
 * 1) We've been discussing my contention that the proper motion he gave (and restored) was wrong, as it was for star A rather than for the common proper motion. At 03:35 on December 31 he removed the number 481.84 mas/y that we've been arguing about, without mentioning it here, and I didn't see it. I still think we should give the components of the common proper motion, as I did.
 * 2) I took out the image showing α Centauri moving toward β Centauri because the angle between the path of α and the line between the present positions of the two is too small. He has restored it.
 * 3) There was the issue of whether we should say that α will be near β "in about 4000 years" or "around 6300 AD" (what I put). But after reverting my edit, he then edited it himself and put "in about 6200 AD", so that's no longer an issue.
 * 4) He wrote, "Worst now in your latest edit, even Kervalla does say what you say and it does and does not give any long term predictions beyond 2050." I don't know what he meant. I think he meant "does not say". I would like an explanation.
 * 5) I removed a lot of unnecessary and unjustified references to Matthews 1994, and he put them back in. If he thinks these are justified, I would like him to quote me the relevant sentences in Matthews.
 * 6) Why did he remove the velocity components I put in? They tell you which way it's moving.
 * 7) Why did he remove the excellent animation I added, showing the path of α Centauri over hundreds of thousands of years.
 * 8) Why did he take out the information about upcoming conjuctions, including a possible Einstein ring, with great value for investigating the α Centauri system?
 * 9) He has now changed the paragraph talking about changes in the orbital elements, but I still want an explanation. I don't think the orbital elements change, although of course the view from Earth of the orbit will change.
 * 10) I contest the statement that α Centauri will end up in the constellation Telescopium.
 * 11) He didn't explain here what he meant in the footnote about θ − θo, but he did edit the article to add the words "Changes ii position anglue (θ) are [calculated as ...]". It doesn't look correct to me, if I understand what the terms are.
 * 12) I would like to know whether there is a reference or an on-line site that we can use to say that the declination at the time of Ptolemy was 53° south.
 * 13) Finally, there's the issue of how close α will get to β. Beta is 4.4° west and 0.16° north of Alpha. Alpha is moving 3620 mas/y westward and 694 mas/y northward. So in 4250 years, it will be 4.27° further west and 0.82° further north, which will be 0.66° north of Beta. Agreed?

Eric Kvaalen (talk) 10:45, 3 January 2018 (UTC)
 * wrote: it will be 4.27° further west and 0.82° further north. No. You're doing a straight cartesian flat-surface addition. A first approximation would be doing the spherical trigonometry instead, but that won't return a precise answer because the proper motions don't stay constant (they change as distance changes - and we'll ignore galactic orbits for periods as short as a few millenia). Doing it right requires doing the 3-D movement of both sets of stars and re-projecting onto the celestial sphere. That's something to be published elsewhere (like, for example, Hartung's). If you are deeply suspicious of a result, doing the calculations can allow you to refute an external source if they are grossly off. But you can't substitute your own results - that has to be published elsewhere. There's a reason for it, we're not set up to do peer review here, and we need to leave these articles in shape so they can be maintained by essentially a modestly knowledgeable librarian not expert in the subject. Tarl N.  ( discuss ) 20:34, 3 January 2018 (UTC)

Look. I have no obligation to do anything. These issues have to be solved so I can do something else. My calculations have verify everything that has been said and agree with the cited references.

1. We've been discussing my contention that the proper motion he gave (and restored) was wrong, as it was for star A rather than for the common proper motion. At 03:35 on December 31 he removed the number 481.84 mas/y that we've been arguing about, without mentioning it here, and I didn't see it. I still think we should give the components of the common proper motion, as I did.
 * A. She using that proper motion was not necessarily wrong. (I actually showed it was mostly irrelevant anyway.) The value requires cpm. NOT pmRA or pmDec. The cpm. determines the stated values of 6.1, 61.3 or 1.02°, and for the precision stated makes little difference to the text.

2. I took out the image showing α Centauri moving toward β Centauri because the angle between the path of α and the line between the present positions of the two is too small. He has restored it.
 * A. The angle of the graphic is fairly correct and agrees with Hartung and is confirmed by my stated calculations above. She knows what she's doing. There is no justification to remove it.

3. There was the issue of whether we should say that α will be near β "in about 4000 years" or "around 6300 AD" (what I put). But after reverting my edit, he then edited it himself and put "in about 6200 AD", so that's no longer an issue.
 * A. The cited reference is what Hartung says. Herself (and you) calculates slightly differently, but it is approximately correct. Is it closest approach or when due north of Beta Centauri is the question.

4. He wrote, "Worst now in your latest edit, even Kervalla does say what you say and it does and does not give any long term predictions beyond 2050." I don't know what he meant. I think he meant "does not say". I would like an explanation.
 * A. She points out that that your added text does not agree with Kevalla, who only extends the discussion to 2050. Kervalla's pm.values are undated source to predict the future cpm. motion of the binary. (We'll add in Kevalla AFTER we get a stable version and sort the problems.)
 * Mostly saying " The proper motion of the centre of mass is about 3620 mas (milli-arcseconds per year toward the west and 694 mas/y towoard the north, giving an overall motion of 3686 mas/y in a direction 11° north of west."
 * 1) Saying "centre of mass" is wrong, as it is based on other factors too. (I've explained that many times
 * 2) "11° north of west." is wrong and not stated. (Direction is better expressed in position angle.)
 * Finally adding this text leaves no explanation of dumping the HIP results expressed in the rest of the article. (I suggested "If you must add the information of Kervalla (2016), then add it to the Star Box, under 'Astrometry', addding the system as 'AB' You should probably also add this to the Distance table at the bottom of the article.")
 * I'm particularly disgusted here as I originally pointed this reference out to you in the first place, then throw it at me. e.g. Quoting you again: "When you say that the values are about -3619.9±3.9 +693.8±3.9 mas/y and that this can be formally cited, what do you mean? What is the source?"

5. I removed a lot of unnecessary and unjustified references to Matthews 1994, and he put them back in. If he thinks these are justified, I would like him to quote me the relevant sentences in Matthews.
 * A. There is no absolutely justification to remove Matthews (1994) here. There are so very few sources on this topic, and explains how to calculate he past and future motion of stars. She thinks you clearly do not comprehend the complexities of the calculations. e.g. (Your own words) "As I said to Tarl, it's an easy calculation to do. All we need are the proper motions of α and β and their present positions." Matthews (1994) is direct evidence of that isn't true.

6. Why did he remove the velocity components I put in? They tell you which way it's moving.
 * A. She removed them because it is not at all relevant

7. Why did he remove the excellent animation I added, showing the path of α Centauri over hundreds of thousands of years.
 * A. She removed the animation because it is wrong and now contradicts the cited references.

8. Why did he take out the information about upcoming conjunctions, including a possible Einstein ring, with great value for investigating the α Centauri system?
 * A. I just cannot see anywhere where you did this. e.g. How can I take out something that is not there?

9. He has now changed the paragraph talking about changes in the orbital elements, but I still want an explanation. I don't think the orbital elements change, although of course the view from Earth of the orbit will change.
 * A. She quotes the statements for the given cited references. e.g. Heintz, W. D. (1978). "Double Stars.", Pub. D. Reidel. p. 19. and W. H. van den Bos (1928) (All that is required of me) As for "I still want an explanation." Tough. Not my problem. I edit here, I do not teach.

10. I contest the statement that α Centauri will end up in the constellation Telescopium.
 * A. Probably said to cause a distraction. Fix pm. info first.

11. He didn't explain here what he meant in the footnote about θ − θo, but he did edit the article to add the words "Changes ii position angle (θ) are [calculated as ...]". It doesn't look correct to me, if I understand what the terms are.
 * A. She quotes the statements for the given cited references. e.g. Heintz, W. D. (1978). "Double Stars.", Pub. D. Reidel. p. 19. and W. H. van den Bos (1928) "It doesn't look correct to me,..." Not my problem. Evidence suggests you are well out of your depth.

12. I would like to know whether there is a reference or an on-line site that we can use to say that the declination at the time of Ptolemy was 53° south.
 * A: Not my problem. (I've given an explanation and two references + agreeing calculations.)

13. Finally, there's the issue of how close α will get to β. Beta is 4.4° west and 0.16° north of Alpha. Alpha is moving 3620 mas/y westward and 694 mas/y northward. So in 4250 years, it will be 4.27° further west and 0.82° further north, which will be 0.66° north of Beta. Agreed?
 * A. No even relevant. Cited reference says 6200AD. What you think or say is totally irrelevant. Considering the effort made by me using the available data such a demand is almost insulting.

As for initially saying (above): "He has not answered most of it, and I contest what he has answered (mostly). " She replies. Days (10 days!) and 8600 words of badgering me for information and you now treat me like this! You are supposed to treat other editors with respect, especially if they are helping you. If you want cooperation you need to smarten up right now. You say " Tarl, I am well aware of the rules of Wikipedia.", well reread WP:Etiquette and WP:INDCRIT again.

Lastly. Now a question you've never answered:
 * "Please explain how you are getting centre of mass pm. of -3649.93, +622.49. " ?


 * Note: Supposedly being French, you'd might think seeing 'Ariane' might just tell you something. As per usual the deliberate gendered 'he' comes out, likely used to put one in their proper place. Really. 2018? Arianewiki1 (talk) 00:45, 4 January 2018 (UTC)

Yes, I know all that. I'm not proposing to put in 0.6° or something, just to take out the 23' which I think I can convince you is wrong. I can do the calculation the way you say, but I predict it won't make much difference in this case. Eric Kvaalen (talk) 14:41, 4 January 2018 (UTC)

I'll answer point by point:

1. "She"? Here I thought you were male. Sorry. (I thought the "Ariane" was for the rocket.)

I repeat, cpm (common proper motion) is not the length of the vector. It's the proper motion that is common to two or more objects.

I still say we should put in the components of the common proper motion (3620 mas/y westward and 694 mas/y northward).

2. User:Skatebiker is also female? How do you know? The angle in the image has a tangent of about 0.1, whereas it should be about 0.66/4.3 or 0.15.

3. "Herself"? Ernst Johannes Hartung was a man!

4. What did I add that doesn't agree witih Kervella? By the way, we certainly can use Keervella's velocity components to predict the position of Alpha Centauri 4000 years from now!

Centre of mass is correct. Kervella et al use the term barycenter.

The arctangent of 694/3620 is about 10.9°. That's not close enough to 11°? And I think most people would understand "11° north of west" better than "towards a position angle of 281°"! I certainly would.

I don't see why you complain about me using the reference that you gave me! And I didn't "throw it at you". I politely asked you for the source. I didn't notice that it was the same number you had given three or four edits earlier. And after asking you for the source, I said, "Let's use that and give the source!"

5. You're using Matthews as a reference for all of the following: Knowing the proper motion of a star or star system allows us to know the great circle that it will travel on. The tangent of the angle from the perihelion varies linearly with time, but if we don't know where on the great circle the perihelion is then we can't say exactly when it will be where. But in our case, we're talking about moving just 4.4 degrees along that great circle, so a simple extrapolation is pretty good. Anyway, we were talking about how close it passes to a given point (the present position of Beta). That we can calculate just from knowing the great circle -- no need to know the timing.
 * As α Centauri approaches its proper motion and parallax increase. (Along with two other references for this obvious fact.)
 * The exact minimum distance of approach to the sun, (I don't see that in Matthews.)
 * That in about 100,000 years, α Centauri will begin to move away from the sun. (I don't see that in Matthews. His diagram shows 30,000 years.)
 * That the path of Alpha Centauri is highly tilted with respect to the plane of the Milky Way. (I don't see that in Matthews and it's not true.)
 * Other stars probably have Oort clouds of their own. (I don't see this in Matthews.)
 * The Oort cloud of Alpha Centauri may have been destroyed already. (I don't see this in Matthews.)

6. The velocity components are interesting information. First of all it tells us that it's moving westward at a similar speed to how fast it's moving toward us. Secondly, it permits someone who want to know to figure out where it will eventually go (not Telescopium!).

7. What cited reference does it contradict??

8. Look at the diff you just gave and search for "Einstein".

9. I don't believe that the cited sources say that the orbital elements change. I cannot access them, so I request that you quote them to us. Otherwise I will put a tag saying "Verification needed".

10. I don't understand. Who said it to cause a distraction?

11. As Ii understand the footnote, it's saying that the position angle of a pair of stars increases linearly with time and proportionally to the proper motion in the easterly direction and to the sine of the right ascension. Doesn't make sense. If you don't put your reference then I will delete it, and if you do then I will tag it "Verification needed".

13. What demand? To tell me whether you agree that 3.620*4250/60/60 ≈ 4.27 and 0.694*4250/60/60 ≈ 0.82? Anyway I was asking.

Thank you for all your help.

How did I get 633.49? Simple. (473.67*1.100+802.98*0.907)/(1.100+0.907). But you said you didn't believe that one can do that knowing the masses alone. Nevertheless, the northward proper motions of A and B times their respective masses times their distance from us (which is practically the same for the two) gives their momenta in that direction. The sum is the momentum for the pair. Dividing that by the total mass and the distance gives the common proper motion in the northward direction. Same for westward direction.

Most Wikipedia editors and most astronomers are male. And most people living in France are French.

Eric Kvaalen (talk) 14:41, 4 January 2018 (UTC)


 * Saying: "I repeat, cpm (common proper motion) is not the length of the vector. It's the proper motion that is common to two or more objects." This is absolutely 110% wrong.


 * "'Common proper motion' is different from a 'common proper motion pair' (read Proper motion), where it is given as:


 * μ = cpm= sqrt ( pmRA^2+pmDec^2) or


 * $$=\sqrt ( {\mu_\delta}^2 + {\mu_}^2 )$$


 * If proper motions of pmRA=-3649.93 pmDec=+622.49 is:


 * sqrt(13321989.0049+387493.80010)=3702.63 mas.yr-1 in PA 279.54° (2014)


 * Proper motion"The proper motion is a two-dimensional vector (because it excludes the component in the direction of the line of sight) and is thus defined by two quantities: its position angle and its magnitude."


 * vector : a quantity having direction as well as magnitude.


 * In knowing distance in parsecs (pc) and common proper motion (μ ), then the tangential velocity (vt) is t=4.74 × d (pc) × cpm (arcsec/yr): Hence:


 * vt = 4.74 × 1.34 × 3702.63 =23517 m.s-1 or 23.517 km.s-1


 * Therefore tangential velocity also changes, and knowing the radial velocity, means we can calculate true space velocity overtime.


 * Matthews (1994) pg.5. 'Table 2' find closest approach as 0.957 parsecs in 28,000 years, when the space velocity is (vs 33km.s-1 and the max magnitude then as -0.7.


 * As radial velocity is then zero, therefore vt=vs.


 * Hence, cpm (say in 28000 yr) (From 33000 = 4.74 × 0.957 × cpm ) is 7274.84 mas.yr-1 (The highest value it will ever get.)


 * This also proves common proper motion (cpm. or μ) is epoch dependent.


 * Simply calculation finds in 6200AD the cpm or μ is now approximately 4793.8 mas.yr-1, whose then estimated pmRA becomes -4725.6 and pmDec +805.9 mas.yr-1 in PA 279.7°


 * If you don't understand even these basics, you do have a serious problem with everything else here. Arianewiki1 (talk) 00:14, 5 January 2018 (UTC)


 * "The Oort cloud of Alpha Centauri may have been destroyed already. (I don't see this in Matthews.)"
 * Right. You do know this refers to the Sun's Oort cloud not Alpha Centauri? (The graphic "Distances of the nearest stars from 20,000 years ago until 80,000 years in the future" shows that.) Matthews pg.6-7 talks about "...some significant perturbative effect on the Solar System." However, the principle does also apply to other stars, even though "As yet there is no direct evidence that such regions do exist around α Centauri AB,". This discussion was added in 2008 to help with astrophysical issues of theoretical planets before any were discovered. Yet, I have now fixed the references and improved these statements to satisfy the complaint..
 * I've also re-added your Einstein ring text and fixed reference. Arianewiki1 (talk) 03:10, 5 January 2018 (UTC)

The article Proper motion says, "Two or more stars, double stars or open star clusters, which are moving in similar directions, exhibit so-called shared or common proper motion (or cpm.), suggesting they may be gravitationally attached or share similar motion in space."

The entry Common proper motion says, "Common proper motion is used to indicate two or more stars that share the same motion through space, within the margin of observational error. That is, they have nearly the same proper motion and radial velocity parameters. This may suggest that they are gravitationally bound or share a common origin." With a reference. (Actually, that sentence that says "they have nearly the same proper motion and radial velocity" is wrong. As I pointed out earlier, α Centauri A and B can have quite different proper motions, for example in 2040 or 1960. I think I'll change that.)

So Matthews does give a closest approach, but a different number from the number you put in our article.

I don't know why you're talking about whether the proper motion changes with time. Everybody knows it does. The magnitude changes, but the object or system continues to move along the same great circle.

I mentioned that one of the places where you cite Matthews was in support of a statement that the Oort cloud of Alpha Centauri may have been destroyed already. You say, "You do know this refers to the Sun's Oort cloud not Alpha Centauri?" Well, no. The sentence was "There is no direct evidence yet of the existence of such an Oort cloud around Alpha Centauri AB, and theoretically this may have been totally destroyed during the system's formation." Now you have removed the reference to Matthews from that sentence and put it on a new sentence, "Such ideas also apply to the close approach of Alpha Centauri or other stars to the Solar System, where in the distant future of our Oort Cloud maybe disrupted enough to see increased numbers of active comets." (I suppose you meant to say " where when in the distant future of our Oort Cloud maybe may be ...".) And you've added a "Citation needed" tag to the sentence about the destruction of the Oort cloud of Alpha Centauri. But you're the one who put that sentence there in the first place. So just take it out!

So, what issues remain?

1. I still say we should give the components of the proper motion of AB.

2. At User talk:Skatebiker has told me that he or she used Stellarium to do that picture. So that doesn't help much. (I understand now that you (Ariane) were calling Skatebiker "she" just to make a point.)

3. No longer an issue. And we have understood why you called Ernst Hartung "herself".

4. No reply since yesterday.

5. You removed two of the references to Matthews and fixed a third. My other three complaints still stand.

6. I still want the velocity components.

7. Still no reference for why the Italian animation is wrong.

8. Conjunctions -- resolved. You added it back, though I haven't checked it yet.

9. No reply since yesterday.

10. No reply since yesterday. I still say it doesn't end up in Telescopium.

11. Still stands.

12. You refused to answer. I suppose you don't know.

13. I would still like  (or you, if you feel up to it) to tell me whether he agrees that if Beta is 4.4° west and 0.16° north of Alpha, and Alpha is moving 3620 mas/y westward and 694 mas/y northward, then in 4250 years, it will be 4.27° further west and 0.82° further north, which will be 0.66° north of Beta. Or shall I do the slightly longer calculation in three-dimensional space, even though we're only talking about a shift of 4.4°?

Eric Kvaalen (talk) 08:40, 5 January 2018 (UTC)


 * Again you have no idea at all.


 * Saying "The article Proper motion says, "Two or more stars, double stars or open star clusters, which are moving in similar directions, exhibit so-called shared or common proper motion (or cpm.), suggesting they may be gravitationally attached or share similar motion in space."

The entry Common proper motion says, "Common proper motion is used to indicate two or more stars that share the same motion through space, within the margin of observational error. That is, they have nearly the same proper motion and radial velocity parameters. This may suggest that they are gravitationally bound or share a common origin." With a reference. (Actually, that sentence that says "they have nearly the same proper motion and radial velocity" is wrong. As I pointed out earlier, α Centauri A and B can have quite different proper motions, for example in 2040 or 1960. I think I'll change that.)" is just utterly ridiculous.


 * Then what do call 'μ' then?


 * As for: "Actually, that sentence that says "they have nearly the same proper motion and radial velocity" is wrong. "
 * PROOF


 * A=−3679.25 473.67 cpm.= −3709.62 mas.yr=1
 * B= −3614.39 802.98 cpm.= −3702.51 mas.yr=1
 * Average is: -3706.05±0.58 3σ'''


 * They do cpm. are nearly equal, aren't they? 09:09, 5 January 2018 (UTC)


 * Another falsehood. "12. You refused to answer. I suppose you don't know." I said " Not my problem. (I've given an explanation and two references + agreeing calculations.) " Lack of comprehension is your problem. You do some work for a change!! Arianewiki1 (talk) 09:14, 5 January 2018 (UTC)

I don't know what term astronomers use for μ. I would call it the total proper motion, or just the proper motion (rather than the components of the proper motion).

As I said earlier, in 2040 the annual proper motions of A and B will be (and were in 1960) about 4" W and 0.3" S for B and 3.3" W and 1.7" N for A. That gives $$\sqrt{3.3^2+1.7^2}\approx 3.7$$ for A and $$\sqrt{4^2+0.3^2}\approx 4.0$$ for B. Anyway, even if the lengths of the vectors were the same, they could be pointing in quite different directions, as in my example.

So you do know a reference or an on-line site that we can use to say that the declination at the time of Ptolemy was 53° south? You haven't given either. All you gave was a couple of computer programs.

You have only addressed (partially) my point 12. What about the others?

Eric Kvaalen (talk) 09:39, 5 January 2018 (UTC)

I have done a bit more thinking and I can prove that Hartung is wrong. (As I said before, I know that we can't put my calculated value into the article, but we can remove the number that Hartung gave.) Let us start with the coordinates of Alpha and Beta as given by Ariane:

α Cen 14h 39m 36.49s -60° 50′ 02.37″ (2000)

β Cen 14h 03m 49.41s -60° 22′ 22.93″ (2000)

Let's first use an equatorial frame of reference with Alpha at longitude zero, so Beta then has a longitude of 35m 47.08s west (of Alpha), which is 8.946°. Let x be the coordinate of Beta on the celestial sphere in the direction 90° west of our zero longitude, y the coordinate in the direction of our zero longitude (the longitude of Alpha), and z the coordinate toward the north celestial pole. So the coordinates of Beta are

x = (cos lat)(sin long) = 0.076875

y = (cos lat)(cos long) = 0.48834

z = sin lat = -.8693

Now let us rotate around the x axis counterclockwise by θ = 60° 50′ 02.37″ to bring Alpha to (0,1,0). This brings Beta to

new x = x

new y = (y cos θ)-(z sin θ) = 0.997037 (This is the cosine of the angle between Alpha and Beta, about 4.4°)

new z = (y sin θ)+(z cos θ) = 0.002794

(Now redefine x, y, and z using x=new x, y=new y, and z=new z.)

Now, according to Kervella, the common proper motion of Alpha is 3619.9±3.9 mas/y westward and 693.8±3.9 mas/y northtward. In order to find the smallest value for the angle between Alpha and Beta at closest approach, let's take a direction which is as far clockwise as allowed with the "plus or minus" given, namely 3923.8 westward and 689.9 northward. Alpha Centauri will continue on the plane slanted at this angle, forever (neglecting curvature of its path due to gravitational forces). So what is the angle between this plane and Beta? Well, we can rotate our system by θ = arc tangent of 689.9/3923.8 to make the plane "horizontal". Then Beta goes to

new x = (x cos θ)+(z sin θ)

new y = y

new z = -(x sin θ)+(z cos θ) = -0.01165

This last number is the negative sine of the number we want, which comes out as 0.667° or 40 arc minutes. (If we want, we can find the other end of the range, using 3616 and 697.7 mas/y. This gives 40.6 arc minutes.) So Hartung's figure of 23 arc minutes is definitely much too small. (Less than the diameter of the moon, whereas the true value is more than the diameter of the moon.) He apparently used old figures for the common proper motion which were not correct. Or maybe he made the mistake of using some value for star A at some epoch!

When Alpha gets to the point closest to Beta in about 400 years, Beta will have moved 33.27×4 ≈ 133 arc seconds west and 23.16×4 ≈ 93 arc seconds south, which means the distance will be a couple arc minutes more than what I have said.

Eric Kvaalen (talk) 19:29, 7 January 2018 (UTC)


 * Eric, on page 347 of More Mathematical Astronomy Morsels (2002) Jean Meeus calculated that the closest approach of Alpha and Beta Cen will be 43 arcmin around the year 5940. He used the proper motion from the FK5, as the Hipparcos value is inaccurate. Your calculation agrees very closely with Meeus, who is a highly reliable authority. So congratulations on getting that right at last! 85.210.96.117 (talk) 21:24, 7 January 2018 (UTC)


 * This edit above seems dubious. The given reference on pg.347 is about planetary groupings in the Solar System, and has nothing to do with closest approach of Alpha and Beta Centauri. (Hence, it cannot be cited.) 85.210.96.117 single edit is suspicious. We heavily rely here on good faith but sockpuppetry is a no-no. Should this be investigated here? Arianewiki1 (talk) 08:48, 10 March 2018 (UTC)

{{Ivmbox| border-s = 20|  Conclusion 

This recent calculation attempts here has so many flaws and wrong terminology, there is no choice but to ignore it just as WP:OR.

Really. This isn't the method to do such co-ordinate transformations and you've just ignored so many other factors. e.g. The changing distance, pm are not constant nor even the U,W, V motions in respect to the Sun. You have been repeated told that it is not a simple calculation to do, but you are still prepared to say "Alpha Centauri will continue on the plane slanted at this angle, forever." Pure fantasy.

Worst you just completely ignore any or all errors. For example, the now almost laughable "How did I get 633.49? Simple. (473.67*1.100+802.98*0.907)/(1.100+0.907). But you said you didn't believe that one can do that knowing the masses alone." Masses are based on the orbital elements or stellar evolution theory and they are error prone. I.e. One or two decimal places at best. Proper motion is based on changes in RA and Dec. Hence, such a properly rounded value would be feasible to be more like 633 or 630. Yet, although it is an approximation, why are the cited reference values around 686±25, 688, 693.8 or 699? Other factors perhaps (which you seemingly claim don't exist)? Even the best known mean proper motions are more like -3608±30 +686±25 (Even Innes in 1905 knew the proper motion was -3642, +699!) Does this now suggest 'your' method is somewhat flawed? Again, it is not as simple as you often have foolishly claimed.

To then outrageously claiming "...I can prove that Hartung is wrong" and "So Hartung's figure of 23 arc minutes is definitely much too small... He apparently used old figures for the common proper motion which were not correct. Or maybe he made the mistake of using some value for star A at some epoch!" is totally unjustified. Hartung value 6200AD and 23′, when you look at the reference he uses -3606, +705 mas. (I was published as 23′N in 5973AD in the 2nd edition and in his 1968 edition 23′N in 6200AD.) A distant approach between α and β Centauri on first approximation is 24′±5′ and is certainly correct. Hartung date has an estimated error by my calculations of about ±300 or ±350 years. It is therefore completely acceptable to quote. Any value of 0.667° or 40′ really seems quite unlikely, simply predicated on the available data being used.

After reading this latest foolish attempt of justification of used sources, based on solely on a lack of your limited understanding to solve the problem(s), I will no longer be responding to any further wild speculations you present. Either starting using the article's required rules in referencing and citing sources, improve the article, or leave the text as it is.

Clue. Such co-ordinate transformations are done as a complex matrix calculation, which also applies to converting any eliptical ecliptical to equatorial coordinates. You also need such as matrix method to show present day Telescopium is the place where α Centauri eventually disappears into the galaxy. Neither are simple to do and rely on various assumptions well beyond abilities of most. You do not have such abilities based on the level of conjecture here.

Furthermore, it's not my job to prove any of this (or explain any other confused or wayward notions.) So please. Stop wasting our time. Arianewiki1 (talk) 02:21, 8 January 2018 (UTC)} }}

I think you meant "ecliptic" not "elliptic" in your next-to-last paragraph.

The changing distance and proper motion have no effect on the calculation.

When you say U, W, V motions, do you mean components in the galactic coordinate system? They are practically constant. As I said, I am ignoring gravitational forces. Actually, I am ignoring gravitational forces other than the gravitational force exerted by the sun. That force doesn't change the plane that I am talking about.

The plane is the plane containing the line from the sun to Alpha Centauri and the ray from Alpha Centauri in its direction of motion. One can also describe it as the plane containing the trajectory of Alpha Centauri and also the sun (or the trajectory of the sun). Alpha Centauri remains on this plane, even if its path is influenced by the gravitational pull of the sun.

The method I used has the advantage of giving the correct minimum separation without having to calculate where Alpha will be as a function of time. We know that Alpha stays on a certain plane going through the sun, and we simply find the angular separation between Beta and that plane (Beta being less than a degree south of the plane).

When I gave the figure of 633.49, I did not mean to imply that it was known to that accuracy. I was simply pointing out that it was much more than the 481.84 that you gave. And I am not ignoring errors. I have calculated the range of the minimum angle as 40 to 40.6 arc minutes (before correcting for the fact that Beta will have moved a little by then).

(I considered doing a calculation including the motion of Beta, but it involves solving a quartic for the times when the separation angle is stationary, which is not easy to express in closed form. There are two real solutions, corresponding to the times of minimum and maximum separation, as well as two imaginary solutions. So I decided to ignore Beta's motion, and then estimate the error from the fact that we know approximately when minimum separation will occur.)

The relative masses of A and B are known much more accurately than what you say. Kervella gives the ratio of the mass of B to the total as 0.45884±0.00027. The paper also gives the ratio found by Pourbaix and Boffin as 0.4617±0.00044. It is the relative masses that are important in calculating the proper motion of the system from the proper motions of the two components.

What do you mean by "when you look at the reference he [Hartung] uses"? There's no reference in the paragraph I quoted.

I am not "attempting to justify used sources". The opposite. I'm saying that the used source is wrong and we should not use it. According to the anonymous editor above, we now have another source that gives the number I found. , what do you think?

Out of curiosity I have just done the calculation of where Alpha Centauri is going. I started with the velocity components given by Kervella, and do two rotations, (one to put Alpha to the correct declination, and a second one to bring it around to the correct right ascension). This gives velocity components of −9.31 km/s towards RA=0 (Pisces), 22.15 towards RA=6 (Orion), and 21.70 towards the north celestial pole. That comes out to a declination of 42.1° N, and an RA of 7.52 hours, on the border between Lynx and Auriga, a point a bit north of the Milky Way. The point of origin (the "radiant point" if you will) is in Sagittarius, just a little north of Telescopium.

Eric Kvaalen (talk) 09:53, 8 January 2018 (UTC)

One might wonder how much the trajectory of Alpha Centauri will deviate (in the plane I mentioned) if the sun is pulling on it. Well (ignoring the influence of other stars), it will move on a hyperbola whose eccentricity is 1 less than the specific angular momentum around the sun times the speed relative to the sun (at perihelion) divided by the gravitational constant and the sum of the masses of the sun and Alpha Centauri. If we express speeds as multiples of the earth's speed around the sun, distance in AU, and mass in terms of solar masses, then this becomes


 * $$e=DV_{pm}V/M_{tot}-1$$

where D is the distance from the sun to Alpha Centauri (276,000 AU), $$V_{pm}$$ is the velocity component perpendicular to the line from the sun to Alpha Centauri (23.38/29.78 = 0.785), V is the speed (at perihelion, but we can use the present value, 32.38/29.78 = 1.09), and $$M_{tot}$$ is 1+2.04. This gives an eccentricity around 77,600. From this we can find the angle by which the trajectory bends:


 * $$\theta=2\arcsin(1/e)$$

which comes to 0.00148°, or 5.3 arc seconds. This corresponds to a change of velocity, perpendicular to the velocity at perihelion, of just 83 cm/s (over the course of tens of thousands of years). Alpha Centauri is of course pulling on the sun with the same force that the sun pulls on Alpha Centauri. Compared to the acceleration of the earth towards the sun, the sun is being accelerated toward Alpha Centauri by $$M_\alpha/D^2$$ or a factor of $2.68$. We can compare this with the force exerted by the Milky Way on the sun, approximately equal to $$V^2/R$$ with V being the speed of the sun around the galaxy (251/29.78 = 8.43) and R being the distance to the centre of the galaxy (8000*206,265 = $1.65$ AU), which comes to $4.3$, a couple thousand times stronger than the pull of Alpha Centauri. The pull exerted by Sagittarius A* (at the centre of the galaxy) on the sun is $$M/R^2$$ with M about four million, giving $1.47$, about 18 times less than the pull exerted by Alpha Centauri.

I suppose Alpha Centauri is the star system exerting the strongest gravitational pull on the sun. It would be interesting to know whether that is true and if so by what factor its pull is greater than that of other stars.

Eric Kvaalen (talk) 07:39, 9 January 2018 (UTC)

I did forget something! Proxima Centauri. It exerts a force on Alpha which causes it to deviate from the trajectory I envisaged, and even from the plane I mentioned. So let's estimate the effect of Proxima over the next 4000 years. It is at a distance of about 12,947 AU from Alpha and has a mass of about 0.122 M☉. That means the acceleration it causes at Alpha is about $7.3$ times the acceleration of the earth going around the sun, which is $$4\pi^2$$ AU per year per year. So Alpha is accelerated toward Proxima by $2.9$ AU per year per year. Multiplying this by 4000 years gives a speed of $1.15$ AU per year. This is the magnitude of a velocity vector which will be added to Alpha's velocity over the next 4000 years. The average over those 4000 years is half of that, and multiplying that by 4000 years tells us that Alpha will be displaced by 0.23 AU by 6000 AD from the position I calculated. That displacement is in a direction towards the southwest and towards us, so the component "in the sky" (that is, towards teh southwest) is less than 0.23 AU. If it were 0.23 AU, then dividing that by the distance, 1.34 pc, we would see this displacement as 0.17 arc seconds. In conclusion, the effect of Proxima over the next 4000 years is negligible.

We may ask how Proxima affects the vanishing point of Alpha. In other words, Alpha and Proxima are a bound system (with a period of half a million years), so to calculate where they are heading we need to find the common proper motion of the whole system. The values for the velocity components (in km/s) for Alpha in the westerly direction, northerly direction, and toward us are:

22.9666 4.4019 22.393

For Proxima they are:

23.268  4.72   22.2

Thus the common velocity components (the weighted averages) are:

22.98   4.42   22.38

This gives for the destination a declination of 42.1° and a right ascension of 7.52 hours, as before. The declination is about 0.001° higher than before and the RA 0.004 hours higher. So again, the effect of Proxima is negligible.

Eric Kvaalen (talk) 06:28, 10 January 2018 (UTC)

, I just edited a paragraph of the article (see edit), improving the English (making it understandable) and removing the footnote which I complained about above (my point #11). 's last reply to me on that was:

She [Ariane referring to herself in the third person] quotes the statements for the given cited references. e.g. Heintz, W. D. (1978). "Double Stars.", Pub. D. Reidel. p. 19. and W. H. van den Bos (1928) "It doesn't look correct to me,..." Not my problem. Evidence suggests you are well out of your depth.

She quickly reverted my whole edit. What do you say?

Eric Kvaalen (talk) 08:06, 26 February 2018 (UTC)


 * As a matter of politeness, you should not guess the gender of an editor. I'm pretty sure Arianewiki1 is male, but that's a guess on my part, assuming the Ariane part comes from Ariane (rocket family). In general, use the editor's userid. If you have to use a pronoun, use "they" (see Singular they), which can be awkward, but avoids mis-guessing on gender (and for what it's worth, I'm male, so you don't have to guess).
 * As to the whole issue of the edit, that entire paragraph to me looks like department of redundancy department. It should probably be removed. I may not be the best judge of that, but for me, the implications of 3d motion (distance gets smaller and larger depending on whether they are moving closer or further away, and the angle of perspective changes) are so obvious as to not need stating.
 * Incidentally, I am really glad you dug up that animation showing the relative position of Alpha Centauri in the sky - a case where a picture is worth more than 1000 words. <b style="color:green">Tarl N.</b> ( discuss ) 16:52, 26 February 2018 (UTC)

I'm opposed to the "singular they" but I agree that generally I shouldn't presume to know the sex of someone. However in this case Ariane made it abundantly clear that she's female, after I made the mistake of using "he" with regard to her (see her contribution of 4 January).

I agree that the paragraph is mostly just obvious or unimportant information, and I was tempted to remove it, but I didn't, fearing a quick reversion! So what do we do now?

Eric Kvaalen (talk) 06:59, 27 February 2018 (UTC)


 * Responses.
 * WP:Canvassing or finding editorial support is unacceptable here.
 * The changes need to be by consensus, and verifiable without WP:OR - original research. No reliable source no consensus.
 * As for the gender, stating it is a two-edged sword. I have my reasons, as in saying it finds different behaviours/attitudes to editors.
 * As for the image, if it is "Source=Own work by uploader; based on data of Fred Schaaf,...", then this too is likely original research and can be rightfully removed. Worst I still think it is wrong. You have to use calculations based on the emerging point and vanishing point of the star relative to the Sun accounting for each body galactic orbits. It isn't linear.
 * This article once said: "Because of visual perspective, about 100,000 years from now, these stars will reach a final vanishing point and slowly disappear among the countless stars." Perhaps that's all needs to be said. Arianewiki1 (talk) 12:41, 27 February 2018 (UTC)

I did not engage in "canvassing". Tarl has contributed several times to this discussion.

We are discussing the fate of the first paragraph in the section "Predicted future changes", on the changes in proper motion, the angular size of the orbit, and position angle. Tarl and I think this paragraph is superfluous, and in any case it's not well written. My compromise was to rewrite it in better English.

Eric Kvaalen (talk) 09:40, 1 March 2018 (UTC)

I have opened a Dispute resolution request. Eric Kvaalen (talk) 09:00, 2 March 2018 (UTC)

The volunteer at "Dispute resolution" closed the dispute with no resolution and suggests we go to "formal mediation". Before we do that, I would like to say that I think there is an error in Heintz (see Google Book link). I think the formula should say:


 * $$\theta-\theta_0=\mu_\alpha(t-t_0)\sin\delta$$

In other words with sin δ instead of sin α (with δ being declination). Could Ariane please give us Equation 3 from his book (which I can't see in Google Books) so that we can check?

Eric Kvaalen (talk) 05:22, 9 March 2018 (UTC)


 * What specific line in the Alpha Centauri article is wrong? This isn't the venue to discuss errors in published material, except where they conflict on statements made in the article. <b style="color:green">Tarl N.</b> ( discuss ) 06:35, 9 March 2018 (UTC)

Well, neither of us likes that whole paragraph which I edited on February 26. But the point of my request that Ariane give us Equation 3 is that the footnote in that paragraph says that $$\theta-\theta_0=\mu_\alpha(t-t_0)\sin\alpha$$ and I think that's a mistake. On the same page in Heintz, a bit higher, there's an equation which is correct (more or less) which correctly has $$\sin\alpha$$ rather than $$\sin\delta$$ and I suppose that may have caused him to make a mistake in the equation we have in our article. Of course, if we take out the whole paragraph then the problem is also solved. Eric Kvaalen (talk) 11:03, 9 March 2018 (UTC)


 * The article says: "'θ − θo = μα × sin α × (t − to ), where; α = right ascension (in degrees), μα is the common proper motion (cpm.) expressed in degrees, and θ and θ''o are the current position angle and calculated position angle at the different epochs."


 * Line p33 in Heintz says Change in position angle by proper motion


 * $\theta-\theta_0=\mu_\alpha \sin \alpha (t-t_0)$


 * Why do you say sin δ, then, when it also appears in Equation 5? The point of the text is it supports that the nodes (Ω) change over time.


 * Eqn. 3 (pg.19) only talks about converting to rectangular co-ordinates : x =ρ cos θ, y= ρ=sin θ.


 * (You can also download a version or read this full article here.) Arianewiki1 (talk) 11:21, 9 March 2018 (UTC)

Comment by Would-Be Mediator
Let me add something. I closed the request for dispute resolution as Failed, not merely as no resolution. I said that formal mediation was one possible next step. I didn't recommend it, because I am not optimistic that an editor or editors who will not cooperate with a first-line volunteer will cooperate with a second-line volunteer. I started out by saying that it appeared that there were mathematical calculations being done that would be original research. In looking over the wall of text here, it again appears either that there is original research, and a demand to include it in Wikipedia, or simply an editor who posts at excessive length without saying anything. In any case, I was initially asked to "Tell us what to do", but the filing editor wouldn't be concise when I said to be concise and say exactly what edits they wanted to make. I said that formal mediation is not likely to work if any of the editors do not coooperate with the mediator, and I already have seen that one of the editors seems to be trying to filibuster the mediation. Go ahead and request formal mediation, but it won't work unless you let it work.

Do not argue that there is an error in a book unless you have a reliable source to that effect. Do not try to get your own calculations into Wikipedia as original research.

Resume discussion on this talk page. As I noted at DRN, it is easier to discuss smaller edits than to discuss a mass rewrite of paragraphs. If a mass rewrite is reverted as no consensus, maybe that is because it is hard to reach consensus on mass rewrites. Robert McClenon (talk) 01:42, 10 March 2018 (UTC)

Or Resume Argument Here
Robert, I did be concise. I said "I think we should drop the whole paragraph and the footnote. It's obvious information (the fact that the orbit looks different as the star system moves by), and not very interesting to those who want to know about Alpha Centauri. I say either drop the paragraph or use my compromise which I did when I edited it on February 26."

If editors can agree that some statement in a reference is false, then it should be taken out. I've had this discussion before and others agree with me. There is no Wikipedia policy that says we cannot do calculations on a talk page in order to show that something in a reference is wrong.

This whole discussion started when I did an edit back in December, and in my edit comment I said that I would explain on the talk page. Then I went to bed, and when I looked in the morning I saw that Ariane had reverted everything. So I wrote here an explanation of all the things I had changed and why. I don't think I should be accused of filibustering for doing that, or for defending what I said. Also in the Dispute resolution thing I tried to do exactly what I was supposed to do.

The edit which I did on February 26 and which was also reverted by Ariane, and which I complained about on the Dispute resolution thing, was just one paragraph. That's all.

Now,, back to you. Thank you very much for the link to the book. I will try to explain (at your request!) why I say the equation is wrong. First of all, I have no problem with his Equation 5. That is concerning the precession of the earth's axis, and so it's right that it depends on the right ascension of the double star in question, because the motion of the double star in equatorial coordinates as the axis of the earth moves depends on where the double star is compared to the equinox (the intersection of the ecliptic with the equator). But the equation which we're discussing (in your footnote) has nothing to do with the position of the ecliptic, so it shoud not depend at all on right ascension. Now, to see how proper motion in the east-west direction affects the position angle, it suffices to take the case of two stars that are initially at RA zero and at declination δ and δ+ε, both at the same distance r from here. Converting to rectangular coordinates, we have
 * $$x=r\cos\delta$$
 * $$y=0$$
 * $$z=r\sin\delta$$

for the first star and
 * $$x=r\cos(\delta+\epsilon)$$
 * $$y=0$$
 * $$z=r\sin(\delta+\epsilon)$$

for the second. Now let them both move $$r\tan(\mu_\alpha(t-t_0))\cos\delta$$ in the y direction. Now the RA of the first star is
 * $$RA=\arctan\frac{r\tan(\mu_\alpha(t-t_0))\cos\delta}{r\cos\delta}=\mu_\alpha(t-t_0)$$

but for the other star it's
 * $$RA=\arctan\frac{r\tan(\mu_\alpha(t-t_0))\cos\delta}{r\cos(\delta+\epsilon)}\sim\mu_\alpha(t-t_0)\frac{\cos\delta}{\cos(\delta+\epsilon)}\sim\mu_\alpha(t-t_0)(1+\epsilon\tan\delta).$$

This is an asymptotic expansion for small ε. Now, in the sky the second star will be approximately ε further north than the first, and $$(\cos\delta)\mu_\alpha(t-t_0)\epsilon\tan\delta$$ further east, so the new position angle is approximately
 * $$\theta\approx\arctan\frac{(\cos\delta)\mu_\alpha(t-t_0)\epsilon\tan\delta}{\epsilon}\approx\mu_\alpha(t-t_0)\sin\delta.$$

Since at the start the position angle was zero, we have:
 * $$\theta-\theta_0\approx\mu_\alpha(t-t_0)\sin\delta$$

as I said. Actually this equation is only valid when the two stars are the same distance from us, but if we talk about the position angle of the line of nodes, then we can write
 * $$\Omega-\Omega_0\approx\mu_\alpha(t-t_0)\sin\delta$$

and this is valid no matter what the inclination is. But of course this is only asymptotically true (for small $$t-t_0$$).

, what do you think?

Ariane, I see that you added a comment about the remark by the anonymous editor. Perhaps he has a different edition of thee book by Meeus. I noticed that there are several editions. Do you have a hard copy? What edition?

Eric Kvaalen (talk) 17:18, 10 March 2018 (UTC)
 * I'm done arguing. If you have a WP:RS to justify a change, cite it and we can discuss it. But this is simply not the venue for arguing that a published source is wrong based on WP:OR. <b style="color:green">Tarl N.</b> ( discuss ) 18:04, 10 March 2018 (UTC)