Define Twilight & its stages?
TWILIGHT
Twilight is the light received from the sun, when the sun is below the horizon, i.e. before the sunrise and after the sunset.
Though the Sun is below the horizon, it illuminates the upper layers of the atmosphere.
Twilight completely ceases in the evening, when the sun is 18° vertically below the horizon. After that, there is total darkness.
Stages Of Twilight
Astronomical Twilight– The time after sunset and before sunrise when the Sun’s centre is in between 12° to 18° below the rational horizon.
Nautical Twilight– The time after sunset and before sunrise when the Sun’s centre is in between 6° to 12° below the rational horizon.
Civil Twilight– The time after sunset and before sunrise when the Sun is below the horizon but Sun’s centre not more than 6° below it.
Sequence of Twilight Occurances
In the Morning – Starts with Astronomical Twilight followed by Nautical and then Civil Twilight.
In the Evening – Starts with Civil Twilight followed by Nautical and then Astronomical Twilight.