Fall begins at 9 p.m. ET on Thursday, a day officially known as the autumnal equinox.
Both the equinoxes and the solstices occur only twice a year – the first days of fall and spring are the equinoxes, and the first days of summer and winter are the solstices.
How are they different?
What is equinox?
On the equinox, the Earth is not tilted toward or away from the Sun, so it gets roughly equal amounts of daylight and darkness, according to the National Weather Service.
In places along the equator, the sun is directly overhead around noon on these days. Day and night appear equally due to the curvature of the sun’s rays, which makes the sun appear above the horizon when it is below it.
During the equinoxes, days are slightly longer at higher latitudes. At the equator, daylight lasts about 12 hours and seven minutes. But in a place at 60 degrees latitude, like the North Pole, a day is about 12 hours and 16 minutes.
What is Solstice?
On the day of the solstice, the Earth is at its maximum tilt, 23.5 degrees, toward or away from the Sun.
During the summer solstice, the Sun is directly above Cancer in the Northern Hemisphere and is tilted toward the Sun, resulting in the longest days of the year. It is winter in the Southern Hemisphere, where the Earth is tilted away from the Sun.
Similarly, the winter solstice occurs in the Northern Hemisphere, the hemisphere tilted away from the Sun, making it a day with less sunlight. The Sun is above Capricorn in the Southern Hemisphere, where the summer solstice occurs.