日照时长计算器
使用此日照时长计算器快速获得准确的计算结果。
Daylight Hours
14.92 hrs
Daylight Hours vs Latitude
公式
Daylight Duration
The number of hours between sunrise and sunset depends on latitude and the Sun's declination (which changes through the year).
Formula
D = (2/15) × arccos(-tan(φ) × tan(δ)) hours
where φ = latitude and δ = solar declination (both in degrees, converted to radians for calculation).
Solar declination ranges from -23.44° (Dec solstice) to +23.44° (Jun solstice).
计算示例
New York (40.7°N) at summer solstice (declination = 23.44°).
- 01cos(H) = -tan(40.7°) × tan(23.44°)
- 02= -0.860 × 0.433 = -0.3726
- 03H = arccos(-0.3726) = 111.86°
- 04D = 2 × 111.86 / 15 = 14.91 hours of daylight
常见问题
What declination should I use?
Solar declination varies from +23.44° (June solstice) to -23.44° (December solstice). At equinoxes it is 0°, giving exactly 12 hours everywhere.
What happens at the Arctic Circle?
At 66.56° latitude, the formula gives 24 hours at summer solstice (midnight sun) and 0 hours at winter solstice (polar night).
Does this include twilight?
No. This gives centre-of-disc sunrise to sunset. Civil twilight adds roughly 30-40 minutes of usable light at each end.