The moment when the sun appears to be crossing the celestial equator is called the equinox.

There are two equinoxes each year:

* Vernal Equinox: Occurs around March 20-21, when the sun moves from the Southern Hemisphere to the Northern Hemisphere.

* Autumnal Equinox: Occurs around September 22-23, when the sun moves from the Northern Hemisphere to the Southern Hemisphere.

During an equinox, day and night are approximately equal in length all over the world.