When is the autumnal equinox? What to know as the days get shorter and weather becomes cooler

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.

While we get ready for cooler weather, expect the leaves to start changing colors from late September to mid-October.

Read on to find out what to know about the autumnal equinox and what you can expect in the days and weeks ahead.

What is the autumnal equinox?

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.

When is the autumnal equinox?

This year, the autumnal equinox falls on Sept. 22 at about 8:05 p.m. EDT.

When will the winter solstice begin?

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 Monday, Dec. 21.

News and CNN contributed to this post.