what is it called when day and night are equal length
Equinox On the day of an equinox, daytime and nighttime 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. The word is derived from the Latin aequinoctium, from aequus (equal) and nox (genitive noctis) (night).
Crepuscular animal Crepuscular animals are those that are active primarily during twilight (that is, the periods of dawn and dusk).[1] This is distinguished from diurnal and nocturnal behavior, where an animal is active during the hours of daylight or the hours of darkness, respectively. The term is not precise, however, as some crepuscular animals may also be active on a moonlit night or during an overcast day. The term matutinal is used for animals that are active only before sunrise, and vespertine for those active only after sunset.