The official beginning of fall in the Northern Hemisphere is on Sept. 22, at 2:19 EST. AccuWeather's Melissa Constanzer explains what happens during the autumnal equinox and why this event occurs.

The official start of astronomical fall is marked by the autumn equinox, a specific moment when day and night are nearly equal in length. This occurs because the Earth's axis is tilted at a 23.5-degree angle, and during the equinox, the axis is neither tilted toward nor away from the sun.

Around the autumn equinox, daylight hours begin to decrease rapidly, especially in the northern hemisphere. Locations such as International Falls can lose over 100 minutes of daylight during September, while cities like Los Angeles and Atlanta lose about an hour. This rapid change in daylight is a direct result of the Earth's position relative to the sun during this period.

Explaining the official beginning of astronomical fall

Break out the pumpkin spice and all things cuddly and nice because the autumn equinox happening Monday, of course, marks the start of fall. It's a specific time that we talk about the start of fall when this equinox occurs because it's when we have equal day and equal night. So why do we have that? Well, you have to think about the axis of the Earth. It's tilted to 23.5 degree angle. And as it makes its trek around the sun, you can see that at some times of the year, we actually have the sun really high up in the northern hemisphere. Other times of the year, not as much. Well, this is a time when the axis is neither tilted towards or away from the sun. Hence why we have the equal time of daylight and darkness around the equinox. It's also when the days are rapidly getting shorter right around the autumnal equinox. And since it falls in the month of September, this is when we stand to lose the most sunlight. If you look at the month of September and say you're in International Falls from the 1st to the 30th, you lose more than 100 days. Meanwhile, in Los Angeles and Atlanta, those cities lose 60 minutes, so an hour worth of daylight. Again, it's a rapid loss of daylight this time of year due to where the equinox falls.

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Washington

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Moscow

Ukraine Invasion

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Lisbon

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Nashua

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Phoenix

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London

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Kyiv

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Tallinn

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Chicago

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Breakdown