The 2017 autumn equinox is here, marking the end of the summer season, as well as the first day of fall for those living in the Northern Hemisphere. Cold weather and longer nights are here.

The equinox signals the official change of season, which occurs Friday Sept. 22 at 4:02 p.m. EDT, according to the U.S. Naval Observatory, which handles astronomical data and serves as the official source of time for the military and country.

On the day of the equinox — a Latin term that means equality between day and night — day and night are each 12 hours long, according to NASA. The U.S. space agency said equinoxes occur when the Earth is in alignment with the sun directly above the Earth’s equator.

Winter officially begins in the Northern Hemisphere this year on Dec. 21.