Here's why:

* Equinoxes mark the two times of year when the sun's rays shine directly on the equator. This means the day and night are approximately equal in length all over the world.

* Equator is an imaginary line that circles the Earth at 0 degrees latitude, dividing the Earth into the Northern and Southern Hemispheres.

So, when the sun is directly over the equator, it's an equinox!