July 1, 2022

the hour of the solstice 2021 is approaching, all you need to know about the phenomenon

WINTER. How was this winter 2021 date set? Why is it the shortest day of the year and the longest night? What is the difference between the solstice and the equinox? But also what are the traditions and cults associated with the winter solstice? Definition, date, pagan festival … Here are answers to the secrets of the winter solstice!

[Mis à jour le 21 décembre 2021 à 11h51] The 2021 winter solstice takes place precisely from 4 p.m., 59 minutes and 19.49 seconds (Paris time) on Tuesday, December 21, 2021, just a few days before Christmas. From this “start” of Mother Nature, the days will begin to lengthen again throughout France … Until the summer solstice, June 21, when the longest day will take place.

Madame Météo has chosen to mark this date by proposing freezing temperatures, a sign that winter 2021 is coming with its first (big) frosts: down to -5 degrees in the Grand Est or in the plain in Rhône-Alpes and no more than 5 degrees maximum over a large part of the North-East of the country. In Brittany, temperatures will not exceed 8 degrees, enough to make this December 21, 2021 the coldest winter solstice day in 15 years according to a meteorologist from Météo France, François Jobard on his Twitter account !

The winter solstice, which therefore corresponds to the shortest day and the longest night of the year, has many meanings. In “Christmas: such a long story“, the historians Alain Cabantous (Paris-I) and François Walter (University of Geneva) stop on a winter solstice considered as the day of birth of the” undefeated sun “, where the daylight starts to grow again. authors, the solstice is indeed the bearer of a “cosmic symbolism” among Christians: it thus becomes for them “the day on which the” true “sun of justice identified with Christ is born. Definition, duration of the day and of the night, rituals around the winter solstice, we take stock of the astronomical phenomenon in our file.

If the winter solstice is less popular than the winter sales, that’s no reason not to be interested in how it works. This winter, our hemisphere will mainly receive grazing rays with a limited heating effect and the North Pole will even find itself plunged into darkness! At the same time, summer will begin in the Southern Hemisphere, with a sun at its zenith above the Tropic of Cancer (each in turn).

During the winter solstice, the position of the Earth in relation to the sun reaches its maximum inclination. Results : the sun seen from our planet is at its southernmost point (the southernmost point in relation to the horizon), the sunshine is as short as possible. During the summer solstice, it is the reverse. The sun is the most northerly and we live then the longest day of the year, marking the arrival of summer. This should not be confused with the autumn or spring equinoxes, during which night and day have the same duration …

Scientifically, the winter solstice corresponds to the time of year when the trajectory of the sun, seen from the earth, reaches its southern (in the northern hemisphere) or northern (in the southern hemisphere) maximum. In other words, in our latitudes, at the time of the winter solstice, the sun rises only 18 ° above the horizon (when during the summer solstice, it is visible at 65 ° altitude, always relative to the horizon ). It is also the day when the inequality of day and night is maximum, with a maximum of night in the northern hemisphere and a maximum of day in the southern hemisphere (which actually lives its summer solstice) . The diagram below will help you to better visualize the phenomenon of the winter solstice (here represented on the right):

The winter solstice is shown on the right. © Peter Hermes Furian / 123RF

The Institute of Celestial Mechanics and Ephemeris Computing (IMCCE) provides the exact date and time of the winter solstice each year. For 2021, according to observations and calculations, the winter solstice therefore begins this Tuesday 21 December at “3:59 p.m. 19.49 seconds” in universal time (UTC), or 4:59 p.m. 19.49 seconds, Paris time.

But how does the Paris Observatory calculate the occurrence of the solstices, which it currently estimates until 2999? In scientific terms, the dates of the seasons are determined from the “geocentric apparent longitude of the sun”: “The winter solstice corresponds to the moment when the geocentric apparent longitude of the Sun is equal to 270 °”, specifies the IMCCE on its site. “Geocentric longitude” is the apparent distance of the sun as seen from Earth.

More prosaically, in our current Gregorian calendar (which is a solar calendar), the winter solstice is likely to occur on December 20, 21, 22, or 23. And most often takes place on December 21 or 22. In our calendar, the length of the seasons varies based on a large period of time: the dates of the seasons are not fixed, but the establishment of a solar calendar has made it possible to limit their drift.

The length of the day and night depend on the latitude as well as the place of residence. Overall, on the day of the winter solstice, it is barely more than 8 hours daylight in the northern hemisphere. For a night which therefore spreads out almost over two-thirds of a 24-hour cycle, i.e. 16 hours!

The event of the solstice is opposed to that of the equinox, the time when day and night are the same duration. The equinox is a time of year that marks the crossing of the sun from one celestial hemisphere to another. On that day, the star passes at the zenith on the Earth’s equator (in other words, the point in the sky at the exact vertical of the equator). The solstice is the opposite of the equinox. It does not mark an equal duration between day and night, but a minimum (winter) or maximum (summer) daylight. And sometimes in the extreme: it’s night all day in the North Pole and day all day in the South Pole! In the northern hemisphere, the spring equinox occurs in March and the fall equinox in September when the solstices occur in June (for the summer solstice) and December (for the winter solstice side). In the southern hemisphere, it’s the other way around! But equinoxes and solstices still have one thing in common: by convention, the dates of the equinox and solstice mark the transition from one season to the next.

The date of the winter solstice marks the onset of astronomical winter, and it is a benchmark in societies for delineating the highlights of the calendar and the seasons. The solstices have therefore been celebrated by many civilizations, from ancient Egypt to Christian societies. We notice, for example, that in Europe, the celebration of Christmas corresponds, to within a few hours, to the time of the year when the northern hemisphere enters winter. In “Noël: Une si longue histoire”, the historians Alain Cabantous (Paris-I) and François Walter (University of Geneva) stop at a winter solstice considered as the birth day of the “undefeated sun”, where the daylight starts growing again. For the authors, the solstice is indeed the bearer of a “cosmic symbolism” among Christians: it thus becomes for them “the day when the” true “sun of justice identified with Christ” is born.
To tell the truth, Christendom relied on a pagan festival, which existed long before we celebrated the coming into the world of Christ. Christmas derives its etymology from Latin birthday day (day of birth), which in the West designated the moment from which the days lengthen again.

The pagan feast from which Christians were inspired corresponds to Saturnalia, these celebrations in honor of the Roman god of sowing and fertility : Saturn. Performed in Ancient Rome, the festivities then spread over seven days, from December 17 to 24. The Romans gathered with family or friends, among vegetation and garlands, and gave each other figurines made of bread or terracotta. The tunic of the poor and the slaves replaced the usual toga. When Julius Caesar reformed the lunar calendar, the “Julian” solar calendar replaced it. And the winter solstice is found improperly set for December 25 (while it takes place on the 21st or 22nd!). The spirit of celebration has indeed remained and has passed through the ages. When you are told that there is reason to be happy …

Today, we hardly celebrate the winter solstice. As Slate explains, the introduction of Christmas on December 25 by Christianity indeed contributed to the disappearance of certain pagan rites that traditionally took place that same month, including yule party, which marked among the Germanic peoples the winter solstice and therefore the arrival of this snow season. This celebration was thus a festival of light since from the winter solstice, the days begin to lengthen. Concretely, the people who still celebrate the feast of Yule today light candles, make fires, go to collect things in nature, make wreaths and give themselves gifts, most often made by hand.

Here are the precise dates and times of the next changes of season causing us to switch to winter, for the years to come, until 2026, in Paris time:

  • December 21, 2022 at 10:48 p.m.
  • December 22, 2023 at 4:27 a.m.
  • December 21, 2024 at 10:20 a.m.
  • December 21, 2025 at 4:03 p.m.
  • December 21, 2026 at 9:50 p.m.