What is twilight and what are they like? At what latitudes are the twilight shortest? The longest?

Twilight is a gradual weakening of daylight after sunset or weakening of night darkness before sunrise, because light is scattered by layers of air that are above the observer’s horizon.
Twilight is: astronomical, navigational, civil.
At the equator, twilight is shortest, as the sun rises and falls perpendicular to the horizon. In the circumpolar regions, twilight is the longest, since the sun moves almost parallel to the horizon.