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)

[edit] Trigonometric Zodiac

Zodiac sign through wihich the Sun passes over time (dates are included for illustration only)

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)

[edit] 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)

[edit] 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)

[edit] 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)