The official first day of fall (2024), also known as the autumnal equinox, is this weekend in the Northern Hemisphere.
Fall officially begins this weekend, though parts of the U.S. have already feeling a sneak peek of the cooler temperatures the season brings. Here are 4 things you need to know about the fall or autumnal equinox:
1. The staring time of Fall on Sunday, Sept. 22, will depend on where you live: If you are in the Pacific time zone, then fall officially begins at 5:43 a.m. The start of fall will be at 8:43 a.m in the Eastern time zone, 5:43 a.m. in the Pacific time zone and 6:43 a.m. in the Mountain time zone.
2. Here’s why there’s a down-to-the-minute time that marks fall’s beginning: According to Encyclopedia Britannica, it is one of only two days, around March 20 or 21 and Sept. 22 or 23, when the sun is directly above the Equator, essentially dividing night and day into equal portions. These are known as vernal equinox and autumnal equinox.
3. Day and night are balanced on the equinox, but daylight will now decrease: During an equinox, the Earth’s axis isn’t tilted toward or away from the sun. Instead, it’s perfectly upright, with the axis of rotation aligned perpendicularly to the line connecting the Earth and the sun.
This results in nearly equal amounts of daylight and nighttime—around 12 hours each—across the globe.
From this point forward, daylight hours in the Northern Hemisphere will start to get shorter, leading up to the winter solstice on December 21, 2024. That’s because the Earth will be tilting away from the sun in the Northern Hemisphere.
4. Everything is opposite for the Southern Hemisphere: Daylight will now grow longer until December’s start of summer in places like Australia and South America, since that part of Earth will receive the sun’s most direct rays.