Talk:Great Year

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"If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. Please do not remove this notice." That seems pretty straightforward to me, yet you deleted the notice yourself without so much as putting a note on the talk page to explain why. Not cricket, that. -- Antaeus Feldspar 05:29, 18 Oct 2004 (UTC)

Couple of questions. Why is it called the Platonic great year. Wasn't precession discovered by Hipparchus after the time of Plato? Wouldn't Ptolemic year make more sense, considering Ptolemy worked on the issue of precession? Second, if the precession of the equinoxes is related to the rotation of the earth's axis around the ecliptic poles, then shouldn't the calculation of the cycle be non-linear: something more like a sine function? My understanding of the Earth's gyration indicates a period of something like 47,000 yeasr. And the gyrating motion would mean the precession would never complete the circle. Instead only six or seven of the zodiac signs would ever see the Sun pass through. I'm going to make some edits accordingly. --Cplot 16:33, 20 June 2006 (UTC)
 * I have no idea why Platonic, maybe he wrote about some philosophies about it. A job for a historian to find out.
 * Concerning your changes: I had to revert them because they were nonsense. Please read the article of the precession of the equinoxes. I think you were confused by the 2 cycles mentioned: the one of 26000 years and the other of 41000. The first one is the precession as such, which goes round and round along the whole ecliptic, passing time and again along all the zodiacal signs, always going on, never going back. The second cycle deals with the speed of the precession. This speed is variable. 50.3" per year now and increasing; but decreasing in 20000 year from now, increasing again in 40000 years and so forth. However the speed never drops below zero (which would mean stillstand and a precession going in the other direction), far from it. --Tauʻolunga 20:00, 20 June 2006 (UTC)


 * I've been researching this topic quite a bit lately and I'm confident of the material I added. My questions were mostly rhetorical. I looked at the rest of the article as you suggest and it says "In reality, more elaborate calculations on the numerical model of solar system shows that the precessional constants have a period of about 41000 years, the same as the obliquity of the ecliptic," which is consistent with what I wrote. As the article elaborates, precession arises from the estimated 41,000 year cycle of the rotation of Earth's axis around the ecliptic pole. That means the it has a 41,000 year cycle. The next question is the nature of that cycle: is it linear or non-linear. You seem to know these trigonometric functions better than I do (from your work on the ecliptic coordinate system article), but if precession occurs because Earth's gyration currently moves with Earth's orbital path, then it should follow that as that gyration moves towards a point perpendicular to the orbital path, the sidereal year will match the tropical year. And therefore the equinoxes will cease their precession at that point. Then as Earth's gyration moves towards the other side of the circle so that its moving in a path opposite the direction of Earth's orbital path, the equinox will occur after the sidereal year (I guess postcession of the equinoxes). Is this original work or does this simply follow from the motion we're talking about here? I expect the cycle would match something like a sine function. This is also consistent with the changing rate of precession as I mentioned in my version. What are your thoughts? --Cplot 06:25, 21 June 2006 (UTC)
 * "In reality, more elaborate calculations on the numerical model of solar system shows that the precessional constants have a period…" Perhaps the wording of this sentence was not clear: the period of 41000 year refers to the constant B in the formula p = A + B * T. This one varies somewhat up and down in 410 centuries, (but always much smaller than A), so that p remains positive forever, and p increases with 360° every 26000 years.
 * Concerning the direction of the gyration while the Earth moves in its orbit around the Sun, and therefore as seen from the Sun, varies over a year. If that would cause the precession, yes it would be varying over a year. But that is not the case. It seems me that in this you make the same error as Abel did in Talk:Precession_of_the_equinoxes. --Tauʻolunga 08:31, 21 June 2006 (UTC)
 * No, I think you misunderstand my point. The function above is a linear function. But look at the motion we're talking about here it's based on the circular movement of Earth's axis. You know better than me that a motion like this cannot be fit to a linear function. The article itself says that the linear function doesn't fit for any significant length of time into the past or the future. That's what happens when one tries to fit a cyclical process to a linear rather than trigonometric function.
 * The article has been reworded to tell that the time dependent factors of p are periodic rather than linear or any polynomial. But the constant term of p will stay forever. --Tauʻolunga 20:10, 21 June 2006 (UTC)

Trigonometric Zodiac
To help visualize what I'm talking about, here's a graph I created to show how the circular motion of Earth's axis would translate into the precession of the equinoxes through the zodiac signs. Sure there would be a constant term to indicate the origin of the graph (relating time to a particular zodiac). However, you can see from the limitations of the functions referred to above, that this cannot fit a quadratic or cubic function: at least not from what we understand of the motion of Earth contributing to the phenomenon.
 * I know exactly what you mean, but your graph and theory do not in any way agree with centuries of measurements, and are therefore to be thrown out immediately without further discussion. You may come back when you have a theory with satisfies the observations. --Tauʻolunga 20:46, 21 June 2006 (UTC)
 * Tauʻolunga, look at the graph. It does match the centuries of observations. It depicts the behavior precisely as the measurments over that short period of time indicated. The problem that this is a cycle that occurs over thousands of years, not hundreds (which is all we have measurments for). We know that it wasn't discovered until Hipparchus and later Ptolemy compared notes. However, the assumption is then made that no one compared notes before them. So there is no data before the equinox passed through Aries. It could be that astronomers were comparing notes for millenia before Ptolemy and Hipparchus, but as you can see from the graph, they would have witnessed very little precession (if anything measurable with their instruments). Also, the speed of precession is increasing: also consistent with my graph. So my graph is consistent with the measurments. I think if you took a little time to step back and consider my arguments and the logic I describe above, you would see how this makes sense. I can tell you know this stuff. --Cplot 21:12, 21 June 2006 (UTC)

I added an update to the garaph. You can see from the horizontal lines that the period over which we have any measurements is quite small. And although this is only an estimated depiction, just from this example you could see how, even if ancient astronomers carefully marked the position of the stars and compared notes, they would not 'discover' precession over a period of thousands of years (because the cycle was coming to a halt). Again, this is only an estimate of the cycle based on perhaps a 20,000 or 25,000 year cycle. If we use the number 41,000 for the periodicty, then the axes would need to be adjusted accordingly (say stretch out the x axis). What do you think?
 * Just take a course in elementary calculus first --Tauʻolunga 00:27, 22 June 2006 (UTC)
 * I've taken courses in calculus among other things. Anyway, I see I forgot to label the scale of my x-axis so maybe that's the block to our communication. I/ve since made some other improvements to the graph and uploaded it here. I think you need to understand the geometry I describe before we start differentiation of the function. We can get to that once we reach an agreement on the motion. Again, the graph is only intended to illustrate the motion of the equionxes through these zodiac signs so the estimates depicted in the graph are just meant to fit the data described in the precession of the equinoxes article. Also as a rough draft of a graph it shows a changing in the cycle over the period covered in the graph. This is more my error in drawing than anything I meant to depict.


 * Just to underscore what I tried to fit in the graph: first, the 41,000 year cycle of the rotation of Earth's axis about its ecliptic; second, the evidence that the rate of precession is increasing which puts Earth on the upward moving portion of the curve between Hipparchus' time and our own; third, I fit the turnaround of the precession just prior to the discovery of the precession. This last point suggests the discovery may have merely been the beginning of precession for our current cycle. Obviously, more precise measure of the precession combined with accurate measures of Earth's orbit and gyration could further narrow the estimates and make a precise mathematical estimate of whre we are in the cycle, but first we must come to terms with this cycle conceptually. --Cplot 03:50, 22 June 2006 (UTC)

Wouldn't a wave like that wraped around an axis be something similar to FM?--207.14.129.217 (talk) 05:46, 17 January 2008 (UTC)

arcsecond units
I might suggest the addition of an explanation of the use of the symbol ". Thinking on it more, I'm expect it means arcseconds, though I'm not positive.  I'm sure it's meaningful to an astronomer or astrologer, but to the average public, it might be thought of as "inches".  I might suggest giving a definition of the symbol before using it extensively.  In addition, if it does mean a portion of an angle, giving that as a measure of speed is likely to be inaccurate.  Speed should be measured over a period of time.  Thanks.  --Sean 07:58, 13 Aug 2006


 * I added a footnote/endnote regarding the units of measure. I also changed the notation to arcseconds to make it less ambigous and more internationally recognized. The quotation mark that was there is a common way to indiccate a quotation, but is an incorrect way to designate an arcsecond. Thanks for pointing thiis out --Cplot 19:57, 13 August 2006 (UTC)

Rise and Fall of Civilisations over approx. 26,000 years cycle
The following paragraph should be removed unless a reference is provided. Most of these ancient cultures believed that during the course of one Great Year civilization will rise for about 12,000 years, culminating in a Golden Age, then fall for 12,000 years, culminating in a Dark Age, before rising again. Thus a Great Year is thought to be a cyclical measurement of time with periods of waxing and waning light and darkness similar to the earth's daily and yearly periods of time Even if a reference is provided at a minimum it its beginning should be changed to: Some of these ancient cultures but to be preicise an example of one or more cultures should be provided.

I intend to remove this paragraph in due course unless some one has an objection Terry MacKinnell (talk) 05:25, 22 March 2008 (UTC)

Should this topic be merges with Astrological Ages?
There does not appear to be any reason why this topic of the Great year should not be merged with Astrological Ages. Terry MacKinnell (talk) 07:22, 3 May 2008 (UTC)

Inadequate References
I have added the inadequate references to this topic as there a numerous facts and details provided but only one reference Terry MacKinnell (talk) 07:06, 17 August 2008 (UTC)

Plato and the great year
Someone asked in 2006 how Plato is involved in all of this. The reason the "Great Year" is also called the "Platonic Year" is that Plato alludes to it in some of his dialogues, for example Republic 546b Timaeus 39d. Pollinosisss (talk) 14:04, 10 September 2009 (UTC)

Great Year, which according to Heraclitus is 10,800 years
Re: "This page is pure BALONEY The Precessional cycle has nothing to do with the Great Year, which according to Heraclitus is 10,800 years. Each time this is pointed out, it gets erased by the astrologists who are bent on imposing their definition of the Great Year on the world.".

There are a number of Great Years including Heraclitus and the Precessional cycle. Why not pre-discuss the appropriate edits to include the 'other' Great Years. Terry Macro (talk) 22:53, 24 November 2009 (UTC)

The Great Year

Heraclitus spoke also of a longer period, which is identified with the "Great Year," and is variously described as lasting 18,000 and 10,800 years. We have no definite statement, however, of what process Heraclitus supposed to take place in the Great Year. The period Of 36,000 years was Babylonian, and 18,000 years is just half that period, a fact which may be connected with Heraclitus's way of dividing all cycles into an "upward and downward path." The Stoics, or some of them, held that the Great Year was the period between one world-conflagration and the next. They were careful, however, to make it a good deal longer than Heraclitus did, and, in any case, we are not entitled without more ado to credit him with the theory of a general conflagration. We must try first to interpret the Great Year on the analogy of the shorter periods discussed already.

- John Burnet, "Early Greek Philosophy," (London, A&C Black, 1920) Terry Macro (talk) 05:20, 25 November 2009 (UTC)

Term 'Great Year'
Does anyone know the origin of the term Great Year? Josephus (Antiquities of the Jews, 1st century CE) writes of a μεγας νιαυτος πληρουτοι of 600 years. Excuse my lack of declension, this seems to translate as a 'Great Full Year'. Whiston and the Loeb translator both give this as 'Great Year' Is there anything earlier?

Despite the NASA definition I think it misleading to equate it with the Platonic Year, the concept may be related to and derived from a cycle specified by Plato but cannot be identical with.

I am afraid the opening is now a bit of a mess, but it's better to be an obvious mess than misleading. Sceptic1954 (talk) 19:41, 17 December 2012 (UTC)

Edits of 16th December
I completely fail to understand the reasoning behind Terry M's reversion. I changed the beginning to give a definition from what is surely a reliable source par excellence, with reference. It's been reverted on grounds I didn't give sufficient reference, to a beginning which has no reference. I find this utterly bizarre. Please can Terry M explain. Sceptic1954 (talk) 23:53, 17 December 2012 (UTC)


 * while NASA may seem like a reliable source, no website is a reliable source. The Great Year topic needs to address all versions of the Great Year.  Your former lede commenced with "The Great Year is the period of one complete cycle of axial precession of the equinoxes around the ecliptic, with a duration of around 25,800 years." - whereas this is only one version of the Great Year.  Terry Macro (talk) 23:20, 18 December 2012 (UTC)


 * This is the first time on Wikipedia I have ever heard anyone argue that 'no website is a reliable source'. The key point is 'reliability'.  I will always try to give a reliable online source as opposed to a paper source, because the former is more easily checked by the reader.  I certainly agree that the article should address all versions and that is what I have tried to do in the opening paragraph. I began with what is to my knowledge the principal contemporary meaning, from a highly reliable source before bringing in others.  It might be helpful that I did not select my user name to demonstrate any particular attitude towards astrology. Sceptic1954 (talk) 23:31, 18 December 2012 (UTC)


 * Sorry, I didn't see your reference to 'my former lead', I have already changed this. I nonetheless think it good to put the NASA definition first, I can't think of any source more 'reliable'. Sceptic1954 (talk) 23:35, 18 December 2012 (UTC)


 * a more concientious editor can certainly pick you up for the mistaken belief that a web reference is a reliable source. A web reference is about the least reliable source that exists to my knowledge (if it is granted any reliability at all).  The fact that an online source is more readily available to the reader is irrelevant to Wiki as a reliable source.  If you don't want another editor to revert your reference to NASA at sometime you should look for a reliable source to back up your statement. Terry Macro (talk) 01:59, 19 December 2012 (UTC)


 * you should read WP:RS and related topics on sources. Using a reference to a website is usually better in the 'See also' or 'External References' etc sections on any topic.


 * I have never seen a wiki editor quote guidelines that online sources are intrinsically less reliable than paper sources - I'd be very grateful if you could quote me where this is the case. To take an example - I've made significant edits to Archimedes which is a former featured article and has 71 references all of them online. I'm not always in agreement on decisions taken by arbitration of what constitutes a reliable 'reliable sources' but NASA must be at the top by any wiki criterion. I don't think there reference is that satisfactory as it brings in 'Platonic Year' without clarification - if you can find a better from a reputable online dictionary please offer it.Sceptic1954 (talk) 06:46, 19 December 2012 (UTC)


 * If you examine the lede to WP:RS it basically commences with the following:

"Definition of source The word "source" as used on Wikipedia has three related meanings: 1. the piece of work itself (the article, book), 2. the creator of the work (the writer, journalist), 3. and the publisher of the work (for example, Random House or Cambridge University Press). Any of the three can affect reliability. Reliable sources may be published materials with a reliable publication process, authors who are regarded as authoritative in relation to the subject, or both. These qualifications should be demonstrable to other people."

It is true that they do include a positive note about reliable websites, but only as an addendum to the main criteria.

Re: 'Platonic Year' without clarification - this is not within Wiki's guidelines. The reference to 'Platonic Year' is a reliable source - if it was from a website, it is harder to prove that it is a reliable source. You cannot disagree with an appropriate book just because you cannot source it online, (though you may readily find the reference in Google Books). You could set up a replica of Wiki online that exclusively uses online sources but that is not Wiki's approach. You should make contact with some other experienced Wiki editors and see what they say - I have set up a topic for discussiopn on this issue at the Talk page at WP:RS or http://en.wikipedia.org/wiki/Wikipedia_talk:Identifying_reliable_sources - see "Are online sources from 'reliable' websites OK when nearly all the references are from these websites and no reference books with page numbers etc cited?" Terry Macro (talk) 02:19, 20 December 2012 (UTC)


 * Before I changed it ther article began with a definition which was unsourced. Sure we now have two definitions from contemporary sources, NASA and Nick Campion, how do we decide which comes first?  I would have thought that NASA comes before Dr Campion, regardless of accessibility, but we could ask a third party.  If an online source and a paper source are equally reliable, I'd put the online sources first as it's easier for readers to access.Sceptic1954 (talk) 09:08, 20 December 2012 (UTC)


 * its up to the editor(s) to decide the relative importance - the article as it stands seems OK to me as long as it covers the different interpretations of the Great Year but i know of one archeo-astronomer (from an American university I believe) that would violently disagree with the NASA definition and has worked on this topic previously. I have done some research, and I cannot find anywhere where Wiki promotes online sources over published reliable sources with author, name of publication and page references.  Where do you find support for your perspective that online sources are better?  I am not into edit wars, but I have experienced many, and somehow i think you will come across an editor(s) at some stage that takes a strong exception to your approach to references.Terry Macro (talk) 23:03, 20 December 2012 (UTC)


 * In case you did not see it, i got a response to my query as follows from the talk page at WP:RS:

"Do sources have to be free, online and/or conveniently available to me? No. Sources can be expensive, print-only, or available only in certain places. A source does not stop being reliable simply because you personally aren't able to obtain a copy. See Wikipedia:Reliable sources/cost. If you need help verifying that a source supports the material in the article, ask for help at Wikipedia:WikiProject Resource Exchange or a relevant WikiProject." I have learnt something new! Terry Macro (talk) 00:48, 22 December 2012 (UTC)


 * Sorry not to reply yesterday, I was out celebrating the End of the World. In the present context question of accessibility is a a red herring.  A source has to be reliable period.  I can't think of any source more reliable according to wikipedia criteria than NASA whether it is online or not.  Everything being equal I'd choose a source which is available online over one which is not.  Have you a source which is not available online which you think it more reliable than the NSSA source. Before my recent edits there were no quoted sources for the definition of the Great Year now there are 3, 2 of which are online,, the remaining one not so.Sceptic1954 (talk) 09:55, 22 December 2012 (UTC)


 * I will get back to you ASAP on your request. Terry Macro (talk) 23:26, 22 December 2012 (UTC)
 * I couldn't find anything in my library. I will keep a look out. Terry Macro (talk) 01:02, 27 December 2012 (UTC)

Magnetic Poles
The long quotation from Finch as regards the true north and magnetic north poles should not be left without an explanation to the effect that he has not a clue what he is jabbering about for the magnetic north pole. The magnetic poles have zero bearing on the issue of precession, though I grant they *may* (or may not) have some contribution to the wobble of Earth. Yes, there are two poles involved in this matter, but they are the true poles of the terrestrial sphere in its rotation and the celestial pole of the ecliptic which has to do with Earth's orbit about the Sun and the tilt of the plane of our orbit. The magnetic poles do not enter into it, at all. Indeed the magnetic north moves independently of Earth's celestial mechanics and has more to do with the behaviour of liquid metal under pressure, the layering of elements in Earth's mantle, the composition of the core, the distribution of land and ocean on our crust (the Arctic as a sea surrounded by land, counterweighted by the Antarctic as a land mass weighed down by ice and surrounded by ocean) and other such matters. The magnetic poles have indeed drifted many hundreds of kilometres over the past two centuries, at a much faster pace than Earth's other poles. As our ice caps melt and shrink, the pace and direction of this drift may accelerate, but that is another topic.BeeTea (talk) 14:46, 8 January 2014 (UTC)


 * I came to the talk page to mention the same thing. I'm no expert, though I believe the Egyptians weren't even aware of magnetic north.  Besides, as you mention, it contradicts the previous statements about the ecliptic north.  Looks like we saw this on the same day a great year apart. :) metric (talk) 12:43, 8 January 2015 (UTC)


 * I have deleted the quote along with the rest of the additions by user jhpalmerjp in the same edit from July 2013. metric (talk) 13:35, 8 January 2015 (UTC)

Length of Great Year
Re the edit change to: The term Great Year has a variety of related meanings. It is defined by NASA as "The period of one complete cycle of the equinoxes around the ecliptic, about 25,800 years or precisely 25,772 years


 * My understanding is that it is not constant, and that the length of the Great Year is consistently decreasing as the Moon slowly increases its orbital distance from the Earth? So while it may be 25,772 years at this point of time, it will be different over the coming centuries? Terry Macro (talk) 01:30, 13 February 2019 (UTC)

Factual accuracy tag
I am now removing this tag as it has been in place since 2014 and the article is in a much better state with many reliable citations.Lumos3 (talk) 17:28, 19 February 2019 (UTC)