but by the way, why is it never the same day?

This year 2022, autumn begins on September 23, compared to two days earlier last year. (illustrative photo) Adobe Stock

This year, the season of red, Halloween and first chills begins on September 23, two days later than in 2021.

Like an unchanging ritual, the days are getting shorter. The trees take on red and orange hues. The leaves litter the soils of cities and countryside. After the strong heat of summer, the first cold spells invite you to change your wardrobe. No doubt possible, autumn is here. If it started on September 21 last year, the date provided for by the Gregorian calendar, change of program in 2022. The painters’ favorite season begins two days later this year, this Friday September 23, therefore, at 1:03 and 40 seconds UTC precisely, or 3:03 and 44 seconds in France, according to the Institute of Celestial Mechanics and Ephemeris Calculation (IMCCE), the French institution dependent on the Sorbonne in charge of producing the ephemeris.

Why such a date difference? The answer lies in an astrological phenomenon: the autumnal equinox, which traditionally marks the start of this new season. It designates the time of the year when the duration of the day is equal to that of the night, ie 12 hours each. To return to the etymology, the word equinox is formed by two Latin terms: “aequus” which means “equal” and “nox, noctis” which refers to “night”.

Two equinoxes per year

There are two of them a year: for the transition from summer to autumn, then from winter to spring. In scientific terms, the beginning of autumn coincides with the passage of the Sun at the zenith of the Earth’s equator, explains the IMCEE.

It remains to explain this shift in dates. To do this, we must go back to the fundamentals of astrophysics. The Earth takes an average of 365 days, 5 hours and 46 minutes to orbit the Sun. A year legally counts 365 days, so you have to make up the difference of a few hours. Hence the need for leap years, every four years, which last 366 days and partially restore the balance. These particular years also have consequences for the dates of the equinoxes. In fact, the beginning of autumn can vary between September 21 and 24, while the spring equinox takes place between March 19 and 21.

Still, this transition to a new season has a direct impact on our lives: from this Friday, the nights will last longer than the days. Throughout autumn, France is expected to lose four minutes of daily sunshine until the winter solstice, described as the day of the year with the longest night. The days will then begin to lengthen again. Phew!

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