The Probert Encyclopaedia of Science & Technology

EQUINOX

An equinox is the precise time when the sun enters one of the equinoctial points, or the first point of Aries about the 21st of March, and the first point of Libra about the 23rd of September, making the day and night of equal length all over the world. At all other times the lengths of the day and of the night are unequal, their difference being the greater the more we approach either pole, while in the same latitude it is everywhere the same.
Research Equinox