Fall officially arrives with the autumnal equinox. What to know.

Fall has arrived.

That means days are getting shorter, the weather is turning cooler, and winter is – gasp – on the horizon. The season will officially begin Monday at 2:19 p.m. Eastern time, the exact moment of the autumnal equinox.

On Monday, the sun will rise due east and set perfectly in the west. The sun’s most direct rays will have crossed into the Southern Hemisphere. South America, much of Africa and Australia are on their way to brighter days and summertime. The Northern Hemisphere will experience the opposite.

The equinox also brings approximate equal daylight and darkness to every place on Earth, with most people experiencing a little over 12 hours of daylight.

The next three months will also represent a transitional period in the atmosphere. The polar vortex will begin to g