Autumn Equinox 2022: why on the 23rd and not the 21st?

Autumn Equinox 2022 why on the 23rd and not the

AUTUMN 2022. Why doesn’t the fall date always correspond to September “21”? How exactly does the astronomical phenomenon of the equinox take place? Here’s everything you need to know about fall.

[Mis à jour le 21 septembre 2022 à 11h46] The equinox is that time when the Sun crosses the plane of our terrestrial equator. In summary : this is the moment when the sun crosses the zenith of the Equator. At that time, we change seasons. The astronomical event therefore closes the summer in the blink of an eye. In the northern hemisphere, it usually occurs between September 21 and 24. But why this year 2022 the season of autumn falls a “23” and not a “22” or a “21”?

If many of us again identify the date of “21” of September as being that of the autumnal equinox, it is not so simple. The date of the passage to autumn corresponds in fact to a very precise moment: that when the Sun cuts through the zenith of the plane of the equator. Scholarly calculations have determined this, 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, the D-Day can change from year to year.

On the day of the equinox, the length of the day is equal to that of the night, but it will no longer be the same as winter approaches with longer nights and longer sunshine durations. reduced. Remember that on average, during the autumn, we lose in France and in temperate regions 4 minutes of sunshine each day! A considerable decrease which is not without consequence on the body… It will be necessary to wait until December 22, date of the winter solstice to see this cycle (finally) stop and that the days start to get longer again. .. In the meantime, let yourself be dazzled by landscapes adorned with purple and ocher, pick mushrooms, chestnuts or walnuts. Discover these little corners of nature in the colors of autumn:

In 2022, the autumnal equinox, as an astronomical event, officially begins on Friday, September 23, 2022. Here are the dates and times of the autumnal equinoxes following the autumnal equinox 2022, estimated until 2025:

  • 2022: September 23 at 1:03 a.m. UT (3:03 a.m.)
  • 2023: September 23 at 6:49 a.m. UT (8:49 a.m.)
  • 2024: September 23 at 12:43 p.m. GMT (2:43 p.m.)
  • 2025: September 22 at 6:19 p.m. UT (8:19 p.m.)

The autumnal equinox of September 23, 2022 takes place precisely at 3 a.m. 3 minutes and 40 seconds French time (1h03 in universal time) according to the Institute of Celestial Mechanics and Ephemeris Calculation (IMCCE). Autumn then continues as every year for three months until winter solstice.

The date of the autumnal equinox precedes the transition to winter time by approximately one month. The first day of autumn also occurs halfway between the summer solstice (June 20-21) and the winter solstice (December 20-21). But each year the autumnal equinox occurs on a different date. This is because the Earth revolves around the sun in 365 days, 5 hours and 46 minutes, and not exactly 365 days. Most of this discrepancy is corrected by the addition of February 29 during the leap years. Mathematically, the fall equinoxes can only occur between September 21 (next time in 2092) and September 24 (next time in 2303).

autumnal equinox
The autumnal equinox 2022 is for September 23. © sborisov –

What is the Equinox? The word comes from Latin aequinoctium (equal night). In effect, for us, the most obvious phenomenon of the equinox is that night and day have the same length at this time of the year. At the autumnal equinox, the days, which lasted about 16 hours on June 21 in France, have largely lost in length. They will thus shorten until the winter solstice. Why ? Due to geometry. In effect, the axis of rotation of the earth is inclined by 23.4° with respect to the plane of its orbit : our planet “leans” in relation to the sun. The star does not illuminate us in the same way depending on the time of year. In winter, France (for example) only receives light for eight hours a day, compared to twice 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 times of the year when the sun is farthest 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!

As’spring equinox, the autumnal equinox is synonymous with rituals each 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. The pagan festivals then symbolize thanks for these famous harvests. In ancient times, after exhausting work in the orchards and fields, this festival was also a welcome break.