As the sun starts to sink earlier and the nights get noticeably longer, you can tell that summer is coming to an end and the first day of fall is coming close! This year, the first day of fall, known as the autumnal equinox, is on September 22.

There are only two equinoxes each year, vernal (spring) and autumnal (fall), with each one marking a day where day and night are about equal. This means that the Sun’s rays are hitting both sides of the Earth’s equator equally and the Earth’s axis (the invisible line around which Earth spins) is tilted directly straight at the Sun.

For centuries, many different cultures around the world have celebrated the equinox. For the Mayans, the equinoxes represented changes in their farming season, and they created the famous Chichen Itza pyramid to honor the importance of the equinoxes. Exactly at sunset on the two equinoxes, the sunlight would hit the staircase of the pyramid at just the right angle to create a snake-like shadow that appeared to slither on the ground!

The equinoxes can also affect which constellations and planets we can see. During this year’s autumnal equinox, watch out for the Fomalhaut, also known as the Autumn Star, that passes through the sky only during the brief period around the autumnal equinox. Overall, the first day of fall is a unique, exciting, and historically significant day that you should be sure to equi-not miss!