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) adobestock

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

Like an immutable ritual, the days grow shorter. The trees take on red and orange hues. The leaves litter the floors of cities and the countryside. After the high summer heat, the first chills invite you to change your wardrobe. certainly possible, fall is the. If it started on September 21 of last year, the date foreseen by the Gregorian calendar, the program will change in 2022. The favorite season of painters begins two days later this year, this Friday, September 23, therefore at 1:03 and 40 seconds. UTC precisely, that is, 3h03 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 so much difference in dates? The answer lies in an astrological phenomenon: the autumnal equinox, which traditionally marks the beginning of this new season. Designates the time of year when the length of the day is equal to that of the night, that is, 12 hours each. Returning to etymology, the word equinox is made up of 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 through the zenith of the terrestrial equator, explains the IMCEE.

It remains to explain this change of dates. To do this, we must go back to the basics 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 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 vernal equinox takes place between March 19 and 21.

Still, this transition to a new season has a direct impact on our lives: starting this Friday, the nights will last longer than the days. Throughout the fall, France is expected to lose four minutes of sunshine daily 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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