For the casual observer, there is no difference between this time and night. It's a time when the Sun is still a light source and prevents the dimmest stars visibility. The last stage is called astronomical twilight. The end of nautical twilight is equal to 102 of zenith angle. It's a time when the horizon line can be seen on the water.
The end of civil twilight is equal to a zenith angle of 96 degrees. It's still quite bright to work without artificial lights indoors at this time. The first stage is called civil twilight. Twilight can be separated into 3 stages, and the end of each of those stages can be used as a sunset point. It's an "official" sunset angle.Īlthough the Sun cannot be seen beyond the horizon, it's often quite bright because of atmospheric reflection. It's 90 degrees 50 minutes at normal atmospheric conditions. But as the Sun is not the point and has its angular diameter and its light reflected by solid particles in the atmosphere, then, to the upper edge of the Sun disappear over the horizon, its center should be a little bit lower than the horizon.
Estimate time until sunset by sun full#
If the Sun was a point and Earth didn't have any atmosphere, then the zenith angle which shows the full sunset, would be 90 degrees. Zenith is a line directed from a point on the earth's surface vertically upwards, and zenith angle is an angle between the vertical and the direction to the center of the celestial object.
I also have to say about the zenith angle, which is set by the "Boundary between day and night" parameter and significantly impacts the calculation. In this case, the calculator shows 24 hours or 0 hours daytime respectively. And you can expect even worse accuracy for places above 80 degrees of latitude.Īlso, for high latitudes, you can encounter a polar day or polar night. However, accuracy degrades for places above 60 degrees of either latitude. This algorithm is said to be correct for the period from 1980 to 2050 and has one-minute accuracy. Source of the algorithm - Almanac for Computers, 1990, published by Nautical Almanac Office, United States Naval Observatory, Washington, DC 20392 Below are calculators for sunrise and sunset.
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