Our long, hot summer is finally coming to an end with the autumnal equinox, which marks the beginning of fall in the Northern Hemisphere.
At a precise moment each September, usually on the 22nd or 23rd, the sun is directly above the equator, marking the autumnal equinox.
When does the autumnal equinox occur?
This year, on Sept. 22, the center of the sun will be directly over the equator at 9:03 p.m. EDT.
In the Northern Hemisphere, the sun will get lower in the sky and days will become shorter until the winter solstice on Dec. 21.
The word "equinox" comes from the Latin words "aequalis" and "nox," meaning "equal night." On the autumnal (and the spring) equinox, day and night are roughly 12 hours long each in most of the world.
What does 'equinox' mean?
12 hours
Earth has seasons because of its tilted axis, which is at 23.5 degrees to its orbit. As the planet rotates the sun, the axis points in the same direction. On Sept. 22, day and night are roughly equal in length.
The Earth's axis: What happens at the poles?
Equinoxes – when day and night are roughly equal – occur in September and March and mark the astronomical beginning of autumn and spring in the Northern Hemisphere, respectively.
What's the difference between an equinox and a solstice?
Solstices occur in December and June, which mark the beginning of astronomical winter and summer, respectively.
The winter solstice occurs when the sun is at its lowest point in the sky, while the summer solstice is when the sun is at its highest point in the sky.
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