On Sun, 9 Jun 2013 07:55:31 -0400, Shmuel Metz (Seymour J.) wrote:
>
>on 06/07/2013 at 02:58 PM, John Gilmore said:
>
>>Leap seconds correct for this precession, keeping UTC seasonally
>>aligned,
>
Sometimes Mr. Gilmore seems to use "precession" in an unconventional
sense. I can find no reference supporting his usage. I'd welcome a
citation.
>Not even close; leap seconds restore alignment of the clock with the
>Earth's rotation; it is leap days that restore seasonal alignment.
>Neither has anything to do with precession.
>
Shmuel is very correct here. I recall the period of precession of the
equinoxes about 26,000 years; this is about 1/3 hour per year.
(Wikipedia says 20m24.5128s longer; I wouldn't have known the
sign.) This is three orders of magnitude greater than the typical
leap second correction, and two or three orders less than the
periodic leap year correction. Neither fits.
http://what-if.xkcd.com/41/
Interestingly, Wikipedia gives the length of the mean tropical
year as 365.242189 days as of year 2000. This is remarkably
close to 365 31/128 = 365.2421875, differing by a fraction of
a second. If Pope Gregory's mathematicians had been less
fixated on powers of 10 and had more precise data they could
have suggested the simpler and more accurate formula that each
year divisible by 4 but not by 128 should be a leap year.
-- gil
o Laskar, J. (1986). Secular terms of the classical planetary theories using
the results of general theory. Astronomy and Astrophysics, 157, 59–70. ISSN
0004-6361.
(unverified Wikipedia citation)
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