CNN Here's a look at the equinox.
The equinox occurs twice a year when the sun is directly above the Earth's equator and days and nights are equal length.
The Northern Hemisphere's vernal equinox occurs on March 19, 20 or 21 in the northern hemisphere. It marks the beginning of spring.
The autumnal equinox occurs in the Northern Hemisphere on February 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.
The term equinox comes from the Latin word equinoxium, meaning equality between day and night. The spring and fall equinoxes have played roles in a number of historical religious and cultural celebrations across the globe.