Only a few days left before enjoying spring.
With the return of softness, no more cocooning in front of a film or a series, make way for walks or bike rides.
This year, the spring equinox falls on Monday March 20 at very precisely 9:24 p.m. and 24 s (Paris time), according to the Institute of Celestial Mechanics and Ephemeris Calculation of the Paris Observatory (IMCCE).
This time corresponds to the precise moment when the sun crosses the plane of the earth's equator.
The duration of the day is then as long as that of the night.
This easily calculated data, to the point that the IMCCE already knows the spring equinoxes until 2999!
But why does the start of the season begin on March 20, and not on March 21 as we were taught at school?
First explanation: the Earth's orbit is not perfectly circular, which means that the seasons have an unequal duration.
Another reason: the Earth goes around the sun in exactly 365.2422 days, and not precisely 365 days.
This small surplus is compensated every four years by leap years, which gives an average year of 365.25 days.
Problem, these leap years compensate too much for this shift.
Thus, approximately every 130 years, the equinox falls one day earlier.
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All dates, month by month
No spring on March 21 before... the year 2102!
During the equinoxes (of spring or autumn), the duration of the day is then as long as that of the night.
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We observe a slow shift towards the beginning of the month which is accentuated at each end of the Gregorian cycle (1600, 2000, 2400 and 2800)
, details the IMCCE.
After each end of the cycle, the number of equinoxes falling on March 19 increases to the detriment of the equinoxes on March 21, then the three following end of centuries there is a shift in dates towards March 20 and 21.
This lag comes from the catch-up of the Julian lag due to the presence of a leap year every four years during the century, the last year of these three centuries not being a leap year, the lag accumulated during the century is brutally compensated.
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The vernal equinox can sometimes fall on March 19, but this is much rarer.
The last time was in 1796. The next time will be in 2044. Readers of these lines will probably never have the opportunity to celebrate spring on March 21: the next one will take place in the next century, in 2102 In other words, in the 21st century, spring will begin almost exclusively on a March 20.
