AUTUMN. The start of the autumn season is marked by the equinox. What exactly does this phenomenon correspond to? At what date and time does it occur?
[Mis à jour le 22 septembre 2024 à 16h28] It’s the beginning of autumn this Sunday, September 22, 2024, since 12:43 p.m. (French time), according to theInstitute of Celestial Mechanics and Ephemeris Calculation located within the Paris Observatory. The season of dead leaves, mushrooms, chestnuts or nuts therefore begins today.
A change of season implies new weather phenomena: the days become shorter than the nights, so there are fewer hours of sun and temperatures begin to drop. The season will last three months, before the start of winter. How can we explain the astronomical phenomenon of the equinox? But also what are the traditions associated with the autumn equinox? Definition, date, time, pagan festival… Here are some answers to the secrets of the autumn equinox!
Why does the autumn equinox 2024 occur on September 22?
The equinox is the moment when the Sun crosses the plane of our Earth’s equator. In summary: This is the moment when the sun passes the zenith of the Equator. At that time, we change seasons. The astronomical event therefore ends the summer in the blink of an eye. In the northern hemisphere, it generally occurs between September 21 and 24. But why will autumn 2026 fall on a “23” and not a “22” or a “21”? If many of us once again identify the date of the “21” of September as that of the autumn equinox, it is not so simple. The date of the transition to autumn actually corresponds to a very precise moment: the moment when the Sun crosses the plane of the equator as it passes at its zenith. Clever calculations have determined it, carried out by the Institute of Celestial Mechanics and Ephemeris Calculation (IMCCE) hosted by the Paris Observatory since 1998. And since the Earth does not revolve around the sun in exactly 365 days, D-Day can change from one year to the next.
Thus, the date of the autumnal equinox precedes the change to standard time by about a month. The first day of autumn also falls halfway between the summer solstice (June 20-21) and the winter solstice (December 20-21). But Every year the autumn equinox occurs on a different date. This is because the Earth orbits the Sun in 365 days, 5 hours and 46 minutes, not exactly 365 days. Most of this discrepancy is corrected by the addition of February 29th during the leap yearsMathematically, the autumnal equinoxes can only occur between September 21 (next in 2092) and September 24 (next in 2303).
What time is the autumn equinox in 2024?
The autumn equinox of September 22, 2024 occurred precisely at 12:00 p.m. 43 minutes and 36 seconds French time according to the Institute of Celestial Mechanics and Ephemeris Calculation (IMCCE). Autumn then continues as every year for three months until winter solstice.
What is the significance of the autumn equinox?
What is the equinox? The word comes from Latin aequinoctium (equal night). Indeedfor us, the most obvious phenomenon of the equinox is that night and day are the same length at this time of year. At the autumn equinox, the days, which lasted about 16 hours on June 21 in France, have largely lost length. They will thus shorten until the winter solstice. Why? Because of geometry. Indeed, The Earth’s axis of rotation is inclined 23.4° relative to the plane of its orbit : our planet “leans” in relation to the sun. The star therefore does not illuminate us in the same way depending on the time of year. In winter, France (for example) receives light for only eight hours per day, compared to double that in summer. This determines the behavior of air masses and gives rise to the seasons as we know them in temperate zones.
But don’t confuse “equinox” with “solstice”. In astronomy, the solstices correspond to the two moments of the year when the sun is furthest from the equator. This corresponds to the maximum duration (for the summer solstice) or minimum (for the winter solstice) of the day. In other words, this phenomenon is very different from that of the equinoxes and their day and night of equivalent duration!
What is the autumn equinox ritual?
Like the spring equinox, the autumn equinox is synonymous with rituals every year in certain cultures or ancient beliefs (followers of druidism and shamanism). Called “Mabon” in Celtic, the astronomical phenomenon designating this moment when day and night have the same duration also corresponds to the time, on the autumn side, when a good part of the agricultural products are harvested. Pagan festivals then symbolize thanks for these famous harvests. In ancient times, after exhausting work in the orchards and fields, this festival also represented a welcome stop.
When will the next autumn equinox occur in 2024 and subsequent years?
Here are the dates and times of the autumn equinoxes for the 2024 autumn equinox, estimated through 2026:
- 2024 : September 22 at 12:43 p.m.
- 2025 : September 22 at 6:19 p.m.
- 2026 : September 23 at 00:05