“No, fall doesn’t start today the 21st”: Why we still have to wait a few days for the new season | Explained – Science

Fall begins on September 21, or so many of us have learned. But is this true? “It’s a misunderstanding that is still very common,” says science expert Martijn Peters. “After all, our seasons don’t always start on the 21st. Astronomical fall won’t start for another two days, on September 23rd.

We can divide our four seasons – spring, summer, fall and winter – in two ways. The easiest is the meteorological classification, also called the meteorological classification. Each season simply begins on the first day of the month. For example, fall runs from September 1 to November 30. Meteorologists have used this classification since 1780, simply because it is so simple.

Confusion about the exact beginning

However, the second method causes a lot of confusion. This is the astronomical division, in which the position of the sun plays a role. For example, spring and fall begin when the sun is directly above the equator in March and September. Then day and night become approximately equal in length. When the sun moves north and is directly over the Tropic of Cancer in June, summer begins. When the sun rises over the Tropic of Capricorn in December, winter begins. These two moments coincide with the longest day or the longest night.

Earth’s axis fluctuates

But in such astrological calculations, the seasons do not always begin on the same day. This is because our calendar year is shorter than the time it takes the Earth to orbit the Sun. This journey takes 5 hours, 59 minutes and 16 seconds, which is longer than 365 days. To adjust for this, we have leap years with an extra day in February.

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Then there is also the Earth’s wobbling axis. It changes very slowly from 21.1 degrees to 24.5 degrees. This takes about 41,000 years. The combination of our calendar and the Earth’s oscillating axis ensures that the beginning of autumn can fall on September 21-24, for example. For example, fall 2023 will start on September 23.

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Megan Vasquez

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