(CNN)Here's a look at what you need to know about the equinox.
The equinox occurs twice per year when the sun is directly above the Earth's equator and day and night are of equal length.
September 23, 2015 at approximately 08:20 UT (universal time) - Autumnal equinox and first day of fall.
The vernal equinox occurs in the Northern Hemisphere on March 19, 20, or 21. It marks the beginning of spring.
The autumnal equinox occurs in the Northern Hemisphere on September 22 or 23. It marks the beginning of fall.
The equinox marks the two times each year when day and night are the same length in all parts of the world.
An equinox is different from a solstice, where the sun hits its northernmost or southernmost position. Solstices mark the beginning of summer (June) and winter (December).
History and Facts:
The term equinox comes from the Latin word equinoxium, meaning "equality between day and night."
Easter always falls on the first Sunday after the first full moon after the vernal equinox.
The spring and fall equinoxes have played roles in a number of historical religious and cultural celebrations across the globe.