This year, the autumnal equinox begins on Sunday September 22, 2024. An important date, eagerly awaited by night owls, but dreaded by sun worshippers. And with good reason: from September 22, 2024, we officially enter autumn, losing an average of 4 minutes of sunshine every day until December 21, the winter solstice.
But what exactly is the equinox? It's an astronomical moment when the length of daylight equals that of night. Every year, two equinoxes take place: one between March 19 and 21, when we move from winter to spring in the northern hemisphere, and the second between September 21 and 24, when we leave summer and enter autumn, again in the northern hemisphere.
The autumnal equinox of 2024 takes place this Sunday, September 22, at precisely 12:43 and 36 seconds (French time), according to theInstitut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE). At that moment, the sun will pass over the zenith of the Earth's equator, rise almost exactly in the east and set due west.
Last year, the autumnal equinox fell on September 23, one day later. By contrast, in 2021, the autumnal equinox fell on September 22, just like in 2020. So why are the date and time never the same? We have to look to our Gregorian calendar to understand. For us, a year lasts 365 days. But in reality, it takes the Earth exactly 365 days, 5 hours and 48 minutes to complete one revolution around the sun. So, to make up for this time lag, we add an extra day every four years - the famous leap years. This shift changes the dates and times of the equinoxes.
Note that the next autumn equinox, scheduled for September 21, will take place in 2092, while the one on September 24 is scheduled for 2303!
