This discussion clears up my confusion. I mistakenly believed, out of a hopefully temporary failure of logical thinking, that every year the sidereal year would always end at the same time of sidereal day. Can't explain how I fell into this misconception. I'm better now!
In checking out a couple of the links and doing some hardcopy reading I found that the tropical year from one spring equinox to the next and the sidereal year measured against the fixed stars differs in length by 20 minutes. The difference is due to precession. 20 minutes is a huge amount and startled me. I did some quick calculations and discovered that every 72 years or so the constellations move by a whole days worth at the spring equinox, approximately a degree. That means that every 2100 years the spring equinox changes constellation, so that in the time of Christ the spring equinox occurred with the Sun in Ares, not Pisces. Wow!
While I knew about precession of the equinoxes, it never impressed itself upon me that it was so incredibly rapid. I had it classified in my mind as a "millions of years" type of process.
--Percy
{Hmmm. This is certainly interesting. I appear to have posted to a thread I've never read. I'll leave this here for now so I can figure out whether it's a bug or user error, and I'll repost this in the correct thread. --Percy}
[This message has been edited by Percy, 01-03-2004]
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