when is the day as long as the night
Equinox On an equinox, day and night are of approximately equal duration all over the planet. They are not exactly equal, however, due to the angular size of the sun and atmospheric refraction. To avoid this ambiguity, the word equilux is sometimes (but rarely) used to mean a day in which the durations of light and darkness are equal.[3][note 1] See Length of equinoctial day and night for further discussion.