Simple Calculation of Sunset Time required

"Dr J R Stockton" wrote in message
nvalid...
In sci.astro message , Wed, 23 Apr
2008 11:51:32, OG posted:

What happened was that back in November 2006 someone was asking about why
the interval between the Winter Solstice and perihelion jittered about
(rather than smoothly progressing).

Plotting the usno times for perihelion (as above) shows two large effects
with obvious explanations
- a 4 year periodic cycle due to leap years
- a slower long term shift in perihelion due to precession of the
equinoxes
see http://www.gwynnefamily.org.uk/astro...lion/index.htm
However, apart from these two effects, there is a third effect (the
jitter
if you like) which would have been of interest to the OP.

The interval, in SI seconds, between the instant of solstice and the
instance of perihelion should be independent of the "daily" rotation
rate of the Earth and of any terrestrial calendar; and, on the time-
scale of the average astronomer, it should be fairly constant. It will
be affected by the perturbing gravity of the rest of the Solar System.

But more by the position angle of the Earth-moon axis with respect to the
Sun

The interval in UTC days (neglecting Leap Seconds) between the two UTC
dates will vary more; and the interval in local civil time will vary
differently-but-similarly away from Greenwich Time.

--
(c) John Stockton, nr London, UK. Turnpike v6.05
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