SPRING EQUINOX. Spring will begin this Monday, March 20, 2023. How was this date set? What time will the astronomical event occur and how to explain it?

[Updated March 20, 2023 at 8:30 a.m.] The spring equinox will officially begin this Monday, March 20, 2023 at 10:24 p.m. and 24 seconds French time. During the vernal equinox day length is equal to night length, but this is not the same as summer approaches with shorter nights and sunshine durations longer. Remember that on average, during the spring, we gain in France and in temperate regions 4 minutes of sunshine every day!

Why does spring, whose first day usually corresponds to March 21 in the collective imagination, arrive in some years a day earlier? What is the difference between Astronomical Spring and Meteorological Spring? But also what are the traditions and cults associated with the vernal equinox? Definition, date, time, pagan festival… Here are answers to the secrets of the vernal equinox!

The season of the first buds, the first rays of sunshine and the first sunburns should start on Monday March 20, 2023. The beginning of spring is marked by milder temperatures “with often more than 15 degrees” in the north of France . But the spring weather can sometimes be more capricious. Late frosts can characterize the first days of spring, as it happens once every 3 to 4 years.

The spring equinox 2023 will take place on Monday, March 20 at 10:24 p.m. and 24 seconds French time (9:24 p.m. and 24 seconds universal time). Astronomically, spring begins around the vernal equinox, which can occur between March 19 and 21. It lasts until the summer solstice. This means that spring lasts about three months. The date of the equinox is calculated for each year by astronomers and mathematicians. It is a question of predicting the exact moment when the plane of the equator and that of the trajectory of the Earth coincide. A calculation made necessary by the discrepancy between our calendar, our time system and the movements of the stars. First, the Earth’s orbit is not perfectly circular, which means that depending on its position in this orbit, the Earth can be more or less close to the sun (between 147 million kilometers minimum and 152 million kilometers maximum). This inevitably makes the duration of each season very irregular and therefore the date of spring variable.

Another explanation: the Earth does not take exactly 365 days to go around the sun. In this our Gregorian calendar, established in the sixteenth century, is much too simplistic. Indeed, it takes 365.2422 days exactly (365 days, 5 hours and 46 minutes) for us to go completely around the star! We are therefore forced to add a February 29 from time to time (during leap years) to correct part (and only part) of this discrepancy. A one-time addition that artificially pushes back the spring date by one day during leap years. This explains why astronomers “advanced” it to March 20 last year. And that the situation arises again this year.

When Caesar established the Julian calendar in 45 BCE, the vernal equinox was set for March 25, based on imprecise observations at the time. But the absence of February 29 in this ancient calendar ended up moving this date to March 11 in the 16th century… It was only when the Gregorian calendar (the one we use today) was established. , in 1582, that a date approaching March 21 was chosen.

The date of “common” spring should not be confused with that of meteorological spring, which begins each year on March 1, allowing meteorologists to make their seasonal calculations on the scale of entire months. In meteorology, spring is considered to begin on March 1 and end on May 31: in this discipline, spring is characterized as a period of warming temperatures (in our latitudes) and increasing duration of the day. It is also one of the most difficult seasons to analyze in this discipline. However, it is the equinox that continues to mark the advent of spring in people’s minds. This is evidenced by the events organized around March 20 in France, starting with the Printemps du Cinéma.

The word equinox comes from the Latin “æquinoctium” (“equal night”) because the most visible phenomenon for man is that the duration of the day becomes identical to that of the night. The reason for this phenomenon? The equinox corresponds to the time of the year when the Sun crosses the equatorial plane of the earth. The star is then at the zenith of the Equator, which allows day and night to share the time equally. And this in both hemispheres, southern and northern. On our side, the days are getting longer and we are halfway between the short days of December and the long days of June. During the equinox, the axis of rotation of the Earth on itself and the axis of rotation of the Earth around the Sun therefore correspond exactly. On our planet, during the equinox, our star appears due east at dawn and disappears due west.

This phenomenon is also related to geometry. The Earth’s axis of rotation is naturally inclined at 23.4° with respect to the plane of its orbit. In other words, our planet “leans” relative to the plane on which it revolves around the Sun (see diagram below). The star therefore illuminates it differently depending on the time of year. This phenomenon explains why the days lengthen or shorten between summer and winter. This also gives rise to the seasons, due to the heating or cooling of the air masses and the oceans according to the time spent each day under the rays of the star. The distance between the sun and the Earth, on the other hand, has no direct link with the temperature. Know for example that the Earth reaches the point closest to the sun (the perihelion) on January 3, ie in the heart of our winter.

The equinox occurs twice a year: between March 19 and 21 (spring or vernal equinox) and between September 22 and 23 (autumn equinox). In spring, the duration of sunshine increases at the equinox to reach 16 hours at the end of June, during the summer solstice. Conversely, the autumnal equinox begins a period of dimming down to just over 8 hours at the winter solstice, around December 21. During the equinox, on the other hand, no jealousy: day and night are supposed to last 12 hours each. However, these data vary slightly since the shape of the Earth is not perfectly regular and the atmosphere slightly deflects the sun’s rays. Thus, in Paris, on March 20, last year, the sun rose at 6:52 a.m. and set at 7:03 p.m. The length of the day was therefore very slightly longer than 12 hours. It is also at the time of the equinoxes that the length of the day increases/decreases the fastest in our latitudes.

Spring equinox and pagan festival are closely linked. Thus, various vernal equinox celebrations around March 21 existed in very ancient times, some of which still survive today. Among them are the bonfires which symbolize liberation from the darkness of winter; or the cakes offered to a deity; when it is not a straw mannequin that is burned or launched, as if to “destroy” winter.