From what I understand, the Precession of the Equinox causes the earth's orientation with respect to the stars to spin (for lack of a better term) every 25,600 years. This would imply approximately a change of 1 degree every 72 years.

Of course we know that there are 365 days in a year so we can roughly assume that 1 degree in Earth's orbit is approximately equal to 1 day.

If I understand Precession of the Equinox correctly. The position of the stars slowly moves because the Equinox is occuring at a slightly different place on earth's orbit every year.

Does this imply that the equinox (and solstice and seasons) is going to move by 1 day every 72 years, or roughly 10 days every 720 years?

Thank you in advance for your help

No, because our calendar is tied to the tropical year (the mean time between one solstice and the next), rather than the sidereal yesr (the time it takes the Earth to return to the same position in its orbit). So the equinoxes will keep the same position in the calendar (averaged over time). What will change is the apparent position of the sun against the background constellations, at the time of equinoxes and solstices.
For instance, the northern spring equinox will stay in late March, but the sun's position at equinox will gradually shift from Pisces to Aquarius.

Grant Hutchison

But that change in the calendar came as a result of the spring equinox occuring earlier and earlier in the year. At the time of Pope Gregory XIII, the equinox was falling on March 17th. This was starting to seriously interfere with the calculation of Easter, so he ordered his astronomers (who, BTW, were working with a geocentric universe) to work out the corrections to the calendar necessary to keep the equinox in place and to put it back on the date that the equinox was first used to calculate Easter--March 21st, 325 AD.

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Keeper of the Jabberwock

Wasn't that because the calendar was a fixed 365-day year, not accounting for the extra 6- hours?

Fred

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"For shame, gentlemen, pack your evidence a little better against another time."
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The Julian calendar, the result of Caesar's reform, has a leap year every fourth year, which would have been perfect if a solar tropical year, the period which includes the correction for precession, were exactly 365.25 days. Since the actual period is about 365.2422 days, a discrepancy of about 10 days accumulated by the late 16th century. Pope Gregory's staff reset the date by arbitrarily dropping 10 days, and decreed that from then on, three leap years would be omitted every four centuries. Thus the years 1700, 1800 and 1900 were not leap years, but 2000 was a leap year.

The Gregorian formula keeps things within a day or so for many centuries. Any further refinement of the formula would be futile because of irregular, unpredictable variations in the Earth's spin rate that would mask it.

D'oh! I knew that (or so I thought).

Fred

__________________
"For shame, gentlemen, pack your evidence a little better against another time."
-- John Dryden, "The Vindication of The Duke of Guise" 1684