View source for Sun Declination


The declination of the sun varies between the Tropics of Cancer and Capricorn depending on the time of year.  This is a measured fact.
This is the approximate formula for the declination of the sun:

S_dec ~=  23.45° x sine( 360°/365 x (d - 81) )
Where: d is the day of the year.

So, for December 2024 solstice:
* January: 31
* February: 29 → total 60
* March: 31 → total 91
* April: 30 → total 121
* May: 31 → total 152
* June: 30 → total 182
* July: 31 → total 213
* August: 31 → total 244
* September: 30 → total 274
* October: 31 → total 305
* November: 30 → total 335
* December: 21 days → total 356

Applying the formula:
* S_dec = 23.45° x sine( 360°/365 x (d - 81) )
* S_dec = 23.45° x sine( 360°/365 x (356 - 81) )
* S_dec = 23.45° x sine( 0.98630137° x (275) )
* S_dec = 23.45° x sine( 271.23287671° )
* S_dec = 23.45° x -0.9997685
* S_dec = -23.44457137°

For December 15, 2024: −23.37°