March 20, 2013, 11:02 UTC
There are two equinoxes every year, for 2013, equinoxes will be in March and September. This events will happen when the sun shines directly on the equator and the length of day and night is nearly the same. Moreover, seasons on this time are opposite on either side of the equator, so the equinox in March is also known as the "spring equinox" in the northern hemisphere. However, in the southern hemisphere, it's known as the "autumnal (fall) equinox".
Why is it called equinox?
On the equinox, night and day are nearly exactly the same length all over the world. This is the reason it's called an "equinox", derived from Latin, meaning "equal night". However, even if this is widely accepted, it isn't entirely true. In reality equinoxes don't have exactly 12 hours of daylight.
