Civil Twilight

[JLB Please excuse me, I'm a Dick. Not a moron just a Dick Find all posts View Profile Close JLB]

You can learn something every day, and for me for today this is it.

And the day is still young.

[vintner Super Moderator Find all posts View Profile Close vintner]

What did you learn today?

[JLB Please excuse me, I'm a Dick. Not a moron just a Dick Find all posts View Profile Close JLB]

The title of my post.

[ArtsieAng Super Moderator Find all posts View Profile Close ArtsieAng]

According to the U.S. Naval Observatory, civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities. Complete darkness, however, ends sometime prior to the beginning of morning civil twilight and begins sometime after the end of evening civil twilight.

Sunrise and sunset conventionally refer to the times when the upper edge of the disk of the Sun is on the horizon, considered unobstructed relative to the location of interest. Atmospheric conditions are assumed to be average, and the location is in a level region on the Earth's surface.