Autumn equinox: what is it?

Cooler temperatures, falling leaves, shorter days… In our hemisphere, the fall equinox heralds the start of a new season. In this year 2022, summer will end like this on Friday, September 23 at 3 in the morning. Back to because of how.

What is the Autumnal Equinox?

The term “equinox” comes from the Latin æquinoctium, from “æequs” (“equal”) and “nox” (“night”). Astronomical phenomenon, designates more commonly (and as its origin suggests) the time of year when the duration of the day is equal to that of the night. as for both solsticesthe shortest day and the longest day of the year, there are two equinoxes in 365 days: thespring equinox and the autumnal equinox.

In the northern hemisphere, the fall equinox marks the beginning of the season of the same name. The days gradually decrease, with a loss of light of approximately four minutes per day, until Winter Solstice December 21. On the contrary, in the southern hemisphere, the days are longer until this date. And for good reason, during its year to go around the sun, the Earth is tilted about 23.4° with respect to the plane of its orbit. The northern hemisphere thus turns towards lightning for half the year, the southern for the other half.

During the equinox, both hemispheres are illuminated in the same way, because the sun is directly over the equator: in astronomy, our star is said to pass through Zenith, point of intersection between the vertical of the equator and the celestial sphere. Therefore, it rises very accurately in the east, to set almost accurately in the west after about 12 hours. The season is changing.

The difference between solstices and equinoxes. Getty Images/Awltail

Autumn equinox: when does it take place?

The date of the autumnal equinox varies from year to year, because our planet revolves around its star in 365 days… 5 hours and 46 minutes, and not just 365 days. The readjustment is done by adding a February 29 every four years (leap years) which changes the date of the equinoxes. Also, as stated above, this corresponds to the precise moment when the sun passes through the zenith. Therefore, calculations and astronomical observations allow the exact moment to be deduced.

Although September 21 is associated with the beginning of fall, mathematically and astronomically, the fall equinox can fall between September 21 and 24 in the Northern Hemisphere. Precedes by about a month the transition towinter time, and is halfway between the summer solstice (June 20-21) and the winter solstice (December 20-21). But it will be necessary to wait until 2092 before it falls on September 21, 2303 on September 24.

In 2022, the autumnal equinox will be celebrated on September 23 at 03:03 and 40 seconds French time (05:03 in universal time), valued the Celestial Mechanics and Ephemeris Calculation Institute (IMCCE), sponsored by theParis Observatory. The season then continues for three months, until the winter solstice.

What is the symbolism of the autumnal equinox?

The transition to fall is associated with traditions and rituals in many cultures around the world. A time to gather a large part of the harvest before the winter frosts, it has long been celebrated by pagans. The “Mabon” name Celtic associated with this equinox, was thus accompanied by festivities of gratitude. In Britain, this is known as the ‘harvest festival’, usually held on the Sunday of full moon closest to the astronomical event, but the date differs according to local celebrations.

During the autumn equinoxes and springthousands of travelers also meet at the Mayan ruins of Chichen Itza (Yucatan, Mexico). Because in the pyramid of Kukulcán (or “El Castillo”) at this same time a game of shadows and lights is created: it reveals a snake, going down or up the 364 steps of the stairway (365 with the entrance to the temple) that forms Monument.

The feathered serpent god (Kukulkan) of the Mayans descending from the pyramid of El Castillo, during an equinox (spring). Getty Images/Borna Mir

Likewise, the republican calendar established on October 6, 1793 by the revolutionaries (and used until 1805) had fixed the autumnal equinox as the first day of the year. Because by chance, the institution of the Republic had taken place on that very day, September 22, 1792, or rather, the 1st Vendemiaire Year I, the day after the abolition of royalty. But it is deleted by Napoleon I when he came to power, he returned to Gregorian calendar.

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