What is a good way to calculate average daylight time between two dates?

Question

Given two dates and a latitude, is it possible to calculate (or accurately estimate) (1) the total amount of daylight / night time between these two days, and (2) the average amount of daylight / night time between the two dates? Any suggestions?! Help much appreciated. Please site your sources, if possible.

Ok then, how then do I calculate or estimate the sunrise/sunset times, given a latitude on any given day?

Also, on that related subject, sunrise/sunset times aren't linear. In other words, the amount of difference between sunrise times near the solstices is smaller than the times near the equinoxes. So, is there a formula or accurate estimation method for calculating the sunrise/sunset times on any given day?

Answer 1

If you want formulas:

d = 23.45 * sin [360 / 365 * (284 + N)]
Where:
d= declination angle of sun, in degrees
N= Day number; Jan 1 = 1, Jan 2 = 2, etc.

Then cos(W0) = (sin(a) - sin(T)×sin(d))/(cos(T)×cos(d))
W0= hour angle of sunset or sunrise
... take negative value for sunrise, positive for sunset
... note that this is local solar time; you will have to correct for
... where you are in your timezone.
a= -0.83 degrees, altitude of the center of the solar disk
T= latitude

Answer 2

Determine the date of sunrise and sunset on each date and on a date in the exact middle between the two. Add the three daylight or night hours together and divide by three. The third date will give you a fix point if you are crossing over a long or short day period.