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Why doesn’t the autumnal equinox fall on the same day every year

Why doesnt the autumnal equinox fall on the same day every year

(ORDO NEWS) — Autumn is just around the corner for everyone in the Northern Hemisphere, while those in the Southern Hemisphere are gearing up for warmer spring weather.

The autumnal equinox can occur anytime from September 21st to 24th, but there has not been an equinox on the extreme dates of this period for more than a hundred years.

Depending on the part of the world you live in, the change of season will take place on September 22 or 23.

This is because the equinox does not last one day. Rather, an equinox is determined by the position of the Earth and the Sun at a particular point in time.

Time zones are not the only source of confusion regarding the date of the equinox. The autumnal equinox can occur anytime between September 21st and 24th – and that makes our calendars even more complicated.

Why are equinox dates always different?

On September 23 at 04:04 Moscow time, the Sun crossed the celestial equator, or an imaginary line that projects the Earth’s equator into space.

At this very moment, the northern and southern hemispheres will receive the same amount of sunlight, and the length of day and night around the world will be approximately the same – hence the term “equinox”.

Usually this happens either on September 22 or 23. However, from time to time, the autumnal equinox may fall on September 21 or 24.

This is because the length of a calendar year (365 days) is not equal to the time it takes the Earth to orbit the Sun (365.25 days).

To compensate for this discrepancy, people have introduced “leap years” and have been using them for the last two millennia.

By adding a “leap day” (February 29) to the calendar every four years, we’ve managed to keep our seasons more or less consistent year after year.

However, leap years do not guarantee that the equinoxes will always fall on the same date. Due to leap years, the dates of the equinoxes and solstices can shift by a day or two over time, causing the start dates of the seasons to shift.

The last time the autumnal equinox was on September 21 was over a thousand years ago, and the last equinox on September 24 was in 1931.

Although it has been a long time since the equinox occurred on September 21st, we can expect it to occur twice this century, first in 2092 and then in 2096. The next equinox on September 24 will be in 2303.


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