Hi,
For a little project I did today, I needed the day's solar declination
for the start, one third gone, and two-thirds gone, of each zodiacal
month (i.e. approximately the 1st, 11th and 21st days of the zodiacal
months).
I treated each of the required dates as a multiple of 10 degrees of
ecliptic longitude, took the sine and multiplied it by 23.44 (for
solstitial solar declination). At first glance, the calculation seems to
have produced results that are adequate for my purposes, but I've got a
suspicion that it's not quite right (because Earth's orbit is an
ellipse, velocity varies, etc.)
My questions: How good or bad was my approximation? Is there a better
approximation/empirical formula, short of doing a complex calculation?
Cheers,
Steve
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