wrote:
I was playing around with Starry Night Pro 5, and I thought I'd see if
I could determine the exact time of the summer solstice by watching
the solar coordinates. With SNP, you can select the sun, bring up an
info panel, and then watch the RA and Dec change as you run through
the clock time at the speed of your choice. I saw some things that I
can't explain, and I hope somebody here can help me.

First, in case my problem is with fundamental knowledge, tell me if
I'm wrong about any of these assumptions:

1) The solstice occurs when the sun reaches its maximum declination of
the year, which should be around 23.5 degrees N. The declination
never decreases between the vernal equinox and the summer solstice,
and never increases between the summer solstice and the autumnal
equinox.



Good thing I looked this up, as I would have been totally wrong!

Explanatory Supplement - Astronomical Almanac

9.211 Equinoxes and Solstices (pg 477)

The times of the equinoxes and solstices are *defined* when the Sun's
*apparent ecliptic longitude* lambda_s is a multiple of 90°; i.e.,
it is calculated from f(t) = 0, where f(t) = lambda_s -0°, 90°, 180°,
or 270°. Thus in the northern hemisphere, for the spring equinox
f(t) = lambda_s, for the summer solstice, f(t) = lambda_s - 90°, for
the autumn equinox f(t) = lambda_s - 180° and for the winter solstice
f(t) = lambda_s - 270°. At the equinoxes the Sun crosses the equator
when the length of the day exceeds the length of the night due to
refraction, semidiameter, and parallax of the Sun. At that time the
lengths of the day and night are approximately equal everywhere.