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My question is basically asking how the vernal equinox changes with time, and how we can track where it will be at certain points in time.

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    $\begingroup$ In 4500 years, some of the constellations are going to look rather different than they do today. Those dang galaxies and stars keep moving! $\endgroup$ Commented Nov 18, 2016 at 13:53

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Due to Earth's axial precession, the vernal equinox gradually travels westward, completing a cycle in roughly 26,000 years, i.e. about 1º every 72 years. Currently, the vernal equinox crosses the ecliptic in Pisces, near its border with Aquarius. In the year 6500, i.e. in 4500 years, it will have moved a further $$ 4500\,\mathrm{yr} \,\, \times \,\, \frac{360º}{26\,000\,\mathrm{yr}} \simeq 62º, $$ that is, to the point that currently has a right ascension of roughly 20 hours. From the map below (from Wikipedia), you can see that it will just have moved out of Capricornus and into Sagittarius.

VE

As @barrycarter made me aware, my first drawing was wrong. Today, the vernal equinox in this map is a vertical line in the right-most edge of the map, going from Polaris in Ursa Minor and through Cepheus, Cassiopeia, etc., down to the Octans. However, due to the precession this map will become distorted, and Polaris will no longer be the Northern Star; instead the axis of Earth will travel roughly along the green line, in the year 6500 lying somewhere in the middle of Cepheus. The Vernal Equinox will lie roughly along the red line, going from Cepheus through Cygnus, Vulpecula, Aquila to Sagittarius.

I drew this line using Stellarium, setting the date to 6500-01-01, switching on equatorial grid of that date and today, and using the orthographic view. My line on the southern sky may be a somewhat imprecise, but on the northern it should be fine.

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  • $\begingroup$ Downvote: you're probably correct in saying that the first point of Aries will move to the specified point in the ecliptic, but the 20h line will look very different then. In particular, both poles precess, and the North Pole does NOT always remain the Little Bear: it will move to the Dragon, the Swan, and many others over time. Same with the South Pole, though I don't know the exact constellations. Your wording also suggests the ecliptic itself will lie in the Little Bear and others, though I think you meant the 20h line. $\endgroup$
    – user21
    Commented Nov 18, 2016 at 17:04
  • $\begingroup$ @barrycarter: Yes, of course, you're right, I hadn't thought of that. However, this doesn't change where the V.E. moves across the map at the zodiac, so it is still true that the V.E. will just have moved into the Sagittarius in 4500 years from now (not 2500, as I wrote). $\endgroup$
    – pela
    Commented Nov 18, 2016 at 22:24
  • $\begingroup$ @DrChuck: Thanks for spotting that. The result is correct, but I wrote the wrong year. $\endgroup$
    – pela
    Commented Nov 18, 2016 at 22:25
  • $\begingroup$ Downvote removed, but I'm still not crazy about your answer with hand-drawn precession circles, sorry. $\endgroup$
    – user21
    Commented Nov 19, 2016 at 17:54
  • $\begingroup$ @barrycarter: Understandable, I like your answer better. $\endgroup$
    – pela
    Commented Nov 19, 2016 at 23:18
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According to Stellarium, the vernal equinox will indeed be in Sagittarius in the year 6500, right around what we call 20h today (actually 19h53m):

enter image description here

The 0h line, however, will look more like this (blue vertical line in the center of the image), and the celestial north pole will be in Cepheus:

enter image description here

and the south celestial pole will be in Carina:

enter image description here

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