Today marks the autumnal equinox, the official first day of fall! While we often think of it as a full-day event, the equinox is actually just a single moment in time. This year, it happened at 2:19 p.m., when the sun crossed the celestial equator—an imaginary line above Earth’s equator—positioning the sun directly overhead.
Normally, Earth’s axis tilts at 23.5 degrees, but at the exact moment of an equinox, it isn’t leaning toward or away from the sun. From this point forward, those of us in the Northern Hemisphere will see the sun rise later, set earlier, and bring shorter days and longer nights until the winter solstice. Interestingly, equinoxes also increase the chances of spotting the northern lights thanks to Earth’s unique positioning.
Why It’s Called an Equinox
The word equinox comes from the Latin phrase meaning “equal night.” Around the globe, day and night are nearly the same length today. However, because of atmospheric refraction, daylight actually lasts slightly longer—anywhere between 12 hours and 6 minutes and 12 hours and 16 minutes depending on where you live.
When the Equinox Happens
The autumnal equinox usually falls on September 22 or 23, though it can occasionally land on the 21st or 24th. This shift happens because Earth doesn’t orbit the sun in exactly 365 days—it takes about 365.25 days, which is why we need leap years. In fact, in 2092 and 2096, the equinox will fall on September 21, something that last happened over a thousand years ago!
A Change in Seasons
From now until December, nights will grow longer and colder, leading up to the winter solstice, the shortest day of the year. After that, daylight slowly begins to increase again. In contrast, the summer solstice marks the longest day, when the sun reaches its highest point in the sky.
Global Traditions and Celebrations
The autumnal equinox has inspired celebrations for centuries.
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In China and across Asia, the Moon Festival is held in mid-September, near the Harvest Moon (the full moon closest to the equinox). Families light lanterns symbolizing prosperity and good fortune and enjoy traditional mooncakes.
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At Stonehenge in England, crowds gather to watch the sunrise on the equinox. It’s one of the rare times each year when visitors are allowed inside the ancient stone circle, a site long thought to have served as a celestial observatory.
Fun Folklore
One quirky myth says you can balance an egg on its end only on the equinox because of special gravitational forces. In reality, you can balance an egg any day of the year—it all depends on the egg and the surface you’re using, not the tilt of Earth.