autumn equinox

12 Hours of Day, Then Night: Autumnal Equinox Explained

This year's Autumnal Equinox falls on September 22, 2022

NBCUniversal Media, LLC

This year's Autumnal Equinox falls on September 22, 2022. But what does that mean exactly?

The Earth rotates on its axis once every 24 hours and revolves around the sun once every 365 days. And because the Earth is tilted at 23.5°, we get four seasons.

When the Northern Hemisphere is tilted toward the sun, we call that the Summer Solstice. This marks the first day of summer in the North and the first day of winter in the South.

One hundred and eighty days later, when the Southern Hemisphere is tilted toward the sun, we call that the Winter Solstice. This marks the first day of winter in the North and the first day of summer in the South.

The halfway points between Solstices are the Autumnal and Vernal Equinoxes.

Because the Earth is neither tilted toward nor away from the sun on these two days, we get direct sunlight over the Equator. This provides approximately 12 hours of day, followed by 12 hours of night.

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