Farewell the long cold winter days and place, this Friday, 20 March, in the spring !
If this change of seasons is a joy for all of us, many people mistakenly think that the first day of spring necessarily arrives on March 21. However, there is not really a precise rule, it can happen between March 19 and 22, depending on the years… Charlie Parisexplains everything in detail !
But do you know why spring day is not always the same ?
For this, we must first look at the astronomical phenomena that govern the changes of seasons.
Our calendar is divided into four seasons, the changes of which are marked by the position of The Sun on the Earth during the solstice (summer, winter) or equinox (autumn, spring).
For the northern hemisphere, the winter solstice takes place on December 20 or 21 and the summer solstice on June 20 or 21. The winter and summer solstices correspond, respectively, to the shortest and longest day of the year.
The equinoxes correspond, on the other hand, to the time when the sun is at its zenith on the Earth's equator, which results in equal sunshine on the southern and Northern Hemisphere. On that day, the duration of sunshine will be almost similar to the duration of non-sunshine. A first equinox takes place between 21 and 23 September and the second Equinox, from spring, between March 19 and 22.
But if these astronomical phenomena appear each, without fail, once a year, why are they not always exactly on the same date ?
To answer this question, we must look at the side of our calendar.
Since the sixteenth century we use to sectionalize time the Gregorian calendarwhich counts on a year 365 days is, in principle, the time that the Earth takes to go around the Sun.
However, the Earth actually takes 365 days, 5 hours and 48 minutes to make a full tour around the sun and not just 365 days.
In order to catch up, we have introduced the leap years. So, once every four years, we add a day to the month of February so that the year has 366 days.
However, the combination of these two offsets means that season changes do not always fall on the same date. If you have a men's watch or a women's watch with the calendar function, be careful to count the days !
If you were convinced that spring was going to drive out winter the 21 March, don't worry, you're not the only one thinking that !
Indeed, this is a fairly common mistake that can be explained by the fact that in The XX century spring fell more often on March 21 (57 times) than on March 20 (52 times).
However, this is an exception confirming the rule, since it will now be necessary to wait until 2102 for spring to fall again on March 21.
So this is not for right away…