Talk:Gaia (spacecraft)/Archive 1

Dates?
What date does Gaia arrive at the L2 point? What date does Gaia start transmitting useful scientific astronomical observation data? What date is anticipated for the first press release or publication of findings? — Preceding unsigned comment added by Robertbowerman (talk • contribs) 12:06, 23 December 2013 (UTC)


 * It looks like Gaia was on-line in July 2014: http://sci.esa.int/gaia/54414-gaia-go-for-science/

Kortoso (talk) 19:07, 30 December 2014 (UTC)

Which L2 again?

 * ... and will be operated in a Lissajous-type orbit around at the second Lagrangian point (L2) of the Sun-Earth-Moon system."

This is ambiguous at best; surely it is supposed to be the Sun-Earth L2 (as opposed to the Earth-Moon L2)? Also misleading, as there is no such thing as a 4th-point Lagrangian point associated with three gravitationally-bound objects. --DWIII 05:25, 4 January 2007 (UTC)
 * Someone fixed; It now says Sun-Earth L2. - Rod57 (talk) 23:01, 14 October 2012 (UTC)

Two problems with this sentence
"Gaia will be launched on a Soyuz-FG rocket and will fly to the Lagrange point L2"

Spacecraft don't fly, do they? There's no air to fly in. Besides, 90%+ of the time, they're coasting.

Also I agree with the above poster. When mentioning Lagrangian points, you need to specify the two bodies involved. Otherwise it's ambiguous. 208.127.118.132 (talk) 20:34, 2 February 2009 (UTC)
 * Well, stop talking about fixing it and fix it. You don't need anyone's permission to do so. PS: in the future, the best place to put your argument is in the edit summary field.U5K0 (talk) 21:07, 2 February 2009 (UTC)
 * I just checked three different dictionaries, and all three explicitly mention spacecraft. The idea that spacecraft don't "actually" fly is, simply, wrong.  That said, if you want to change it, and the result is still accurate, I doubt if anyone will object.  Xtifr tälk 20:39, 24 June 2011 (UTC)

Sound strange
It is written that the mission will last 5 years, will check 1 billions stars, each start will be observed on average 70 times. So, I made the following calculation (70*1,000,000,000)/(5*365*24*60*60)=444. This satelite can really observe 444 stars a second??? I hardly believe it. any source/proof? Froggy helps ;-) (talk) 14:01, 11 September 2009 (UTC)
 * The article says that the satellite has 106 CCDs each 4500x1966 pixels, thats roughly 938 million pixels. With a camera of that resolution 444 stars a second seems quite slow.


 * Apparently, Gaia is quite fast at recording stars. THE GAIA ON-BOARD SCIENTIFIC DATA HANDLING, Fr´ed´eric Arenou et al, mentions 10 Video Processing Units each of which exceed 1.7 million samples per second. One section assumes 55 stars/sec on each CCD, and there are 62 astrometric field CCDs so that is 3410 stars per second. That is only an average; on dense fields (galactic center) the number would be much higher. Note also: "The size of the focal plane is 420mm x 850mm (see Fig. 4). It consists of 14 Sky Mapper (SM) CCDs, 62 Astrometric Field (AF) CCDs, 7 CCDs for the Blue Photometer (BP), 7 for the Red Photometer (RP), and 12 for the Radial Velocity Spectrometer (RVS). Additionally, two CCDs are used for the Wave Front Sensor and two for the Basic Angle Monitor." -from The Gaia Project - technique, performance and status   Bealevideo (talk) 17:53, 9 April 2010 (UTC)

What does V stand for?
Is it magnitude as in apparent magnitude? --Memming (talk) 16:42, 10 September 2011 (UTC)


 * Although i'm struggling to find it stated in the sources in so many words, apparent magnitude would make more sense in this context yes. ChiZeroOne (talk) 20:41, 10 September 2011 (UTC)

Extra-solar planets
How will it "Measure the orbits and inclinations of a thousand extrasolar planets accurately, determining their true masses" - the same as Kepler (spacecraft) or better ? Extrasolar_planets says Gaia will use astrometry. (presumably the intermittent observations don't allow transits or radial velocity changes to be used. - Rod57 (talk) 23:49, 14 October 2012 (UTC)


 * I just added a reference to a paper by Casertano et al. (2008), which describes a performance assessment study in great detail -- Aepsil0n (talk) 14:55, 8 November 2012 (UTC)
 * Thank you - very helpful - Says Gaia planned to precess; (Would allow more regular observations) so I guess Gaia should be able to detect elliptical wobbles around the stars mean proper motion after allowing for the annual parallax. - Rod57 (talk) 18:27, 19 June 2016 (UTC)

Design to reduce cost
The BBC source says " first feasibility work on Gaia in the late 1990s. Back then, the thought was for a huge satellite carrying two camera arrays incorporating some 500 CCDs. "I think the key point that made it feasible was being able to compress the instrument down to just a single focal plane such that it would fit into a Soyuz [rocket] and wouldn't require an Ariane 5, and therefore could be done within the cost budget that Esa had in mind" Jordan2008 says "The basic design of Gaia has been described by Perryman et al. (2001) and ESA (2000). However, in 2002 a major reduction in size, complexity, and cost ... was made." Might be worth mentioning - esp' if we can get a source for the original size and cost estimates. ? - Rod57 (talk) 11:55, 15 October 2012 (UTC)

More citations needed
I've added a cn tag to the statement:


 * Determine the distances to the nearest stars within 0.001%, and to stars near the galactic center, 30,000 light years away, within 20%

this also needs some clarification: what do the percentages mean? Accuracy? In that case it should read within xx% accuracy. Perhaps a Refimprove tag should be added to the top of the article seeing that many more references are needed? Regards. Gaba (talk)  12:10, 9 September 2013 (UTC)


 * In agreement with the above, I note that elsewhere it is said: "determining the positions, distances, and annual proper motions of 1 billion stars with an accuracy of about 20 µas (microarcsecond) at 15 mag, and 200 µas at 20 mag" and I don't understand how this is compatible with the above quotation. TomS TDotO (talk) 14:23, 9 September 2013 (UTC)


 * Ok, seeing as nobody opposed, I'm adding the Refimprove tag to let people know this article needs more sources. Regards. Gaba  (talk)  13:45, 10 September 2013 (UTC)

That line about precision of distance measurements which contains incorrect numbers was added to the article by User:TomS TDotO in 2010 in the edit https://en.wikipedia.org/w/index.php?title=Gaia_%28spacecraft%29&oldid=387765285

The article ESA Bulletin 103: GAIA – Unravelling the Origin and Evolution of Our Galaxy, M.A.C. Perryman, O. Pace, August 2000 contains the following numbers: ''About 20 million stars will be measured with a distance precision of 1% and about 200 million will be measured to better than 10%. Distances accurate to 10% will be achieved as far away as the Galactic Centre, 30 000 light-years away.'' Astredita (talk) 14:07, 29 September 2013 (UTC)

New sources
This article [http://adsabs.harvard.edu/abs/2013arXiv1309.2157B The Gaia astrophysical parameters inference system (Apsis). Pre-launch description] was published today in arXiv and it looks like a good reference to use for some of the info presented in the article unreferenced. Don't really have time right now but I'll be taking a look later, I'm leaving it here so others can give it a read too. Cheers. Gaba (talk)  13:42, 10 September 2013 (UTC)


 * A new release with graphics: . Cheers, BatteryIncluded (talk) 16:31, 21 October 2013 (UTC)

Mission description
"The mission aims to compile a 3D space catalogue of approximately 1 billion stars, or roughly 1% of stars in the Milky Way"

Why 1 billion? Because the rest are too far out, so no parallax will be detectable? Because the rest are too faint, so Gaia won´t see them? How should anyone know it´ll be a billion, if most of them will be seen for the first time? Will the mission stop when it´s found a billion?

That is stupid ad-talk, aimed at people who are stupid. It´s not a mission target. Nobody will care if it gets 500 million or 2.5 billion stars.

The article never states if Gaia will scan the whole sky. Somewhere down it says that it wants to find over a billion stars with magnitude < 20. Does that mean all stars < 20? --Maxus96 (talk) 21:56, 11 September 2013 (UTC)
 * 1 billion is an estimate of the number of stars the mission will be capable of collecting data from. What do you mean by "whole sky" and "all" stars? Also, the childish use of curse words is not only unnecessary it lowers the chances that you'll get a response by several factors. Gaba  (talk)  22:17, 11 September 2013 (UTC)
 * No. 1 billion is the expected number of stars that will be catalogued. Gaia is capable of finding stars down to mag20. Sorry, but that´s exactly to what i object. Imprecise language leaves the reader with the feeling that he hasn´t fully understood what he just read. Some people will then think "author was stupid" or "i´m too stupid", senators might think "they´re trying to fool me, better cut their funding". Ooops.
 * I really hate that, sorry.
 * what´s unclear about "whole sky" and "all stars [with mag] <20"? --Maxus96 (talk) 22:03, 15 October 2013 (UTC)


 * Well speaking of imprecise language, the above is inaccurate too.... ~1 Billion is the number of stars for which Gaia should acquire data with the goal precision. It is a mission target, that's why there are goal precisions, because the whole point of Gaia is to do population analysis requiring a defined sample including a statistically significant set of a variety of stars at different stages of their evolution. Gaia will actually catalogue more stars, perhaps around ~2 Billion, but with less constraints on their properties such as the parallax for example. Also I'm not sure what Senators have to do with an ESA mission... ChiZeroOne (talk) 16:38, 16 October 2013 (UTC)


 * Imprecise language manifests if an article about a survey mission does not contain the word "survey", but instead throws about numbers that the average educated reader cannot appraise, especially as the region in the sky that is to be surveyed is still not mentioned.
 * Have you read the first senctence in Astronomical survey? "... is a general map ... which lacks a specific observational target." The only valid target for a survey is a goal precision, and this strictly excludes targeting a number. You´re mixing up scientific results with preliminary guessing. If we knew the number, there would be a lot less need to do the survey!
 * And, please: There is nothing "statistical" about an all-sky survey. The number of stars Gaia will find determines the errorbars on your population analysis. It´s not a fairy where you can wish for a certain errorbar lenght. --Maxus96 (talk) 01:42, 15 June 2014 (UTC)

All stars that can be observed by Gaia can be seen with other telescopes - as an example, the Hubble telescope can see stars that are too faint for Gaia. Hubble is just unable to observe the whole sky with a reasonable precision. It can observe small parts of it, and based on those parts it is possible to calculate the number of stars Gaia will observe. Yes, the other stars are too faint to be seen. --mfb (talk) 11:48, 23 October 2013 (UTC)

How much data will Gaia generate / transmit?
The article presently says that 60TB will be transmitted, and the uncompressed size of that data is 200TB. That data is not in the nearest cited article,, as far as I saw. According to the ESA's blog, 1PB of data will be transmitted—see under heading "The Gaia data storm"JeffEpler (talk) 02:30, 30 October 2013 (UTC)


 * Difficult one, depends specifically what is being talked about. If you view the recently updated operations page it says;
 * "A total of some 100 Terabytes of science data will be collected during Gaia's lifetime. The estimated total data archive will surpass 1 Petabyte, roughly equivalent to 1000 1-Terabyte hard drives from a top-end home PC."
 * So maybe they are including engineering data in the Petabyte estimate. ChiZeroOne (talk) 18:46, 30 October 2013 (UTC)

"Precision of 1%"
The terminology in the objectives section is somewhat confusing. Is phrasing such as "distance precision of 1%" a standard I am not familiar with? As a casual reader with no background in this field, that phrasing makes me think the precision is only 1% accurate, but from the context it sounds more like 1% would be the margin of error. Is there any way we could make this part more accessible? Some guy (talk) 01:45, 20 December 2013 (UTC)

Unmanned
As a lay reader coming to this article about a "spacecraft"/"space observatory" the first question I had was how many personnel it requires. This information should be given to readers immediately (not after going over the whole thing where there is still no mention of personnel) and I propose the word "unmanned" in the first sentence.--Gibson Flying V (talk) 05:17, 20 December 2013 (UTC)
 * Done.--Gibson Flying V (talk) 08:10, 20 December 2013 (UTC)

Diagram to translate
Please verify the English translation is technical and makes sense:


 * BatteryIncluded (talk) 14:08, 23 December 2013 (UTC)

Good primary source
Leaving it here in case anyone wants to mine it for data: The design and performance of the Gaia photometric system. Regards. Gaba (talk)  19:30, 25 August 2014 (UTC)

Note on parallax precision - correct?
Am I correct in thinking that the note on the parallax/astrometric accuracy may be miscalculated?

> For comparison, Gaia could measure the distance of a 15th magnitude star 10 parsecs (32.6 light years) from the Earth with an accuracy of 0.0002 parsecs (0.000632 light years), another such star 1000 parsecs (3260 light years) from the Earth with an accuracy of 0.02 parsecs (0.0632 light years.)

If the parallax accuracy is 20 µas for magnitude 15 (from the main text, see also first table in science performance), then it will measure the 10 parsec star's parallax as 100 +- 0.02 mas (an 0.02% error), giving a distance of 10 +- 0.002 pc, and the 1000 parsec star as 1 +- 0.02 mas (a 2% error), giving a distance of 1000 +- 20 pc, no?

Willhsmit (talk) 01:05, 24 September 2015 (UTC)
 * I agree. Looks like someone did wrong original research there. The numbers also disagree with the sourced statement "Distances accurate to 10% will be achieved [...] 30,000 light-years away." --mfb (talk) 11:50, 24 September 2015 (UTC)
 * See also the Measurement Principles section. Maybe just take out that footnote?  The text that the note is attached to appears to be correct. Lithopsian (talk) 12:53, 24 September 2015 (UTC)
 * I removed it. --mfb (talk) 13:49, 24 September 2015 (UTC)

2015 HP116
Should it be mentioned in the article that Gaia was mis-identified as near-Earth asteroid 2015 HP116? -- Kheider (talk) 04:37, 4 October 2015 (UTC)

Will Gaia use Secular parallax or just annual parallax
Will Gaia measure or use Secular parallax or just annual parallax ? Could be why they need a few years data (rather than just one) to determine proper motion ? - Rod57 (talk) 13:34, 19 June 2016 (UTC)

What attitude control
Article mentions "fine pointing" but this may be misleading as presumably the spin axis is never fixed. ... Casertano2008 says " (precession angle around the Sun direction 50°, precession speed of the satellite's spin axis 5.22 rev yr-1, spin axis rotation speed 60 arcsec s-1)," - (amended) Rod57 (talk) 18:01, 19 June 2016 (UTC)

How will its exoplanet finding capabilities compare to Kepler
How will Gaia's exoplanet finding capabilities (over the whole sky) compare to Kepler_(spacecraft)'s on target regions ? - Rod57 (talk) 14:16, 19 June 2016 (UTC)