Ask Storm Team: What is twilight?


Twilight is the period of time between before sunrise and after sunset. During these times, the atmosphere is not completely lit nor completely dark. 

There are three categories of twilight which depend on how far the sun is from the horizon.

Civil Twilight is when the center of the sun is 6 degrees below the horizon. During civil twilight, the brightest stars and planets can be seen. The horizon and terrestrial objects can still be recognized. This is when streetlights usually come on and people turn the lights on to drive their cars. 

Nautical Twilight is when the center of the sun is between 6 & 12 degrees below the horizon. The term gets its name from sailors being able to take reliable readings from well-known stars and the horizon is still visible. Here, terrestrial objects may still be recognizable. 

Astronomical Twilight is when the center of the sun is between 12 & 18 degrees below the horizon. Most people would consider the sky completely dark at this time as sky illumination is very faint. Here the horizon is not discernible and most stars and planets that are typically visible are. 

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