Calculate day length for a latitude and date.
Day length depends on the interaction between latitude and solar declination. At the equator it barely varies, while above sixty degrees the swing exceeds twelve hours between solstices. This is why high-latitude summers have usable light until late evening while the same places lose most of the working day in winter.
Daylight Duration
Day length = 2 × arccos(−tan(latitude) × tan(declination)) ÷ 15
Day length = 2 × arccos(−tan(latitude) × tan(declination)) ÷ 15 Day length depends on the interaction between latitude and solar declination. At the equator it barely varies, while above sixty degrees the swing exceeds twelve hours between solstices.
This is why high-latitude summers have usable light until late evening while the same places lose most of the working day in winter.
This calculator takes 2 inputs: Latitude, Day of the year. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.