Fall begins on Monday, September 22 when the Sun crosses the celestial equator in the sky heading south.
The first moment of autumn will be 10:29 p.m. EDT, according to astronomers at the Pisgah Astronomical Research Institute.
“What is the astronomical significance of this moment? At this moment the Sun in its apparent path around the sky will stand directly over the equator of the Earth. It is one of two times during the year when this happens, the other being on the first day of spring,” the nonprofit said.
“These are the two days of the year when the Sun is above the horizon for exactly half the day and is below the horizon an equal amount of time. Thus, the length of daylight is equal to that of the night (neglecting twilight) and this day is termed the equinox from the Latin for ‘equal night.’”
After the equinox, there’s less and less daylight each day until the winter solstice in December--this year slated for December 21.
After the solstice days get longer until the spring equinox in March--next year on March 20.
The National Weather Service notes that the equinoxes are the only two times of the year when the Earth’s axis is tilted neither toward nor away from the sun, resulting in a “nearly” equal amount of daylight and darkness at all latitudes.
“The ‘nearly’ equal hours of day and night is due to refraction of sunlight or a bending of the light’s rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon,” it says.
While those south of the equator will begin to enjoy longer days and warmer weather, people in the United States and other parts of the world will have to deal with increasingly shorter days and increasingly cold weather.
