Even if the leaves haven't yet begun turning where you live, Labor Day is over, school is back in session and fall is almost here. The official arrival of the season is the autumnal equinox, which occurs in the Northern Hemisphere this month.
After a hot summer, the September equinox marks a welcome shift in the seasons for many folks. But what exactly is an equinox? It's all about Earth and its relationship with the sun. Here's how to understand, visualize and celebrate the autumnal equinox.
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When is the autumn equinox?
This year, the autumnal equinox in the Northern Hemisphere falls on Monday, Sept. 22. If you want to be extra specific and mark it on your calendar, mark it for 11:19 a.m. PT.
Dates can shift slightly for equinoxes depending on the year, but it's always around this time in September. The next vernal equinox in the Northern Hemisphere takes place on March 20, 2026, and will mark the start of spring.
What is the autumn equinox?
The meaning of equinox is right there in the name: a combination of the Latin words for equal and night.
"There are 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 National Weather Service said in an explainer about the seasons.
A NASA illustration shows the angle of Earth's tilt in relation to the sun. NASA's Goddard Space Flight Center
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