On Friday, September 22, 2017, we’ll be welcoming autumn and saying farewell to the Summer of 2017.

Fall officially arrives at 4:02pm ET.

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.