Chillier weather, shorter days, hot mugs of apple cider and Halloween decorations aren't the only signs the seasons are changing. It's officially the first day of fall, based on astronomical data.
Read on to find out what to know about the autumnal equinox and what you can expect in the days and weeks ahead.
According to NASA, the term "equinox" derives from the Latin words for "equal" and "night" and refers to the alignment of the sun and Earth.
In the fall, the autumnal equinox occurs when the center of the sun passes Earth's equator, and on the day of the equinox, the sun will be directly overhead at noon, according to NASA.
During an equinox, sunlight shines, for the most part, equally in the Northern Hemisphere and Southern Hemisphere, and both the North Pole and South Pole are lit up at the same time.
In the Northern Hemisphere, the equinox symbolizes the onset of shorter days with longer, cooler nights, while in the Southern Hemisphere, spring arrives with longer, warmer days.
This year, the autumnal equinox falls on Sept. 22 at about 2:19 p.m. EDT or 11:19 a.m. PDT.
The last time there was an equinox this year was the start of spring, on March 20.
As the sun continues to pass Earth, it will travel in a southward direction until the winter solstice in December. After that, the sun will move again in a northern direction.
According to the Royal Museums Greenwich in the U.K. and the Adler Planetarium in Chicago, the winter solstice this year is expected on Dec. 21.
