sin(a) = sin(0) = 0 = sin(L)sin(6) + cos(L)cos(8)cos(hss)
where hss is taken as positive at sunset.
Since the hour angle at local solar noon is 0°, with each 15° of longitude equivalent to 1 h, the sunrise and sunset time in hours from local solar noon is then
The sunrise and sunset hour angles for various latitudes are shown in Figure A3.1 in Appendix 3.
The day length is twice the sunset hour, since the solar noon is at the middle of the sunrise and sunset hours. Therefore, the length of the day in hours is
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