It’s time to say goodbye to Summer and hello to Autumn. Fall officially rolled in at 3:50am ET this morning.

The timing of the four seasons is determined by shifting sunlight, which on its own is determined by how our planet orbits the Sun and the tilt of its axis. Half-way between summer and winter, autumn will see days getting shorter and temperatures getting colder throughout the northern hemisphere (while the days will be getting warmer in the southern hemisphere.)

To simplify things, meteorologists use dates other than the equinox to determine the start/end dates of weather seasons. The first day of meteorological autumn arrived September 1 and ends November 30.

If you’re eager for winter, you can begin the countdown to the next season. This year, winter will begin on Saturday, December 21, at 11:19pm ET.