Spring doesn’t always start on March 21st, it can also occur on the 20th or more rarely on the 19th! This date therefore varies depending on the year and we will explain why.

After a particularly rainy winter where the sun was very shy, spring made its comeback, bringing with it mild temperatures and the promise of beautiful sunny days. This year again, spring arrived on March 20th and not on the 21st of the month as most of us learned at school. In fact, the last time we welcomed the spring equinox on March 21 was in 2007!

Since 2008, spring begins on March 20 each year, but this situation is far from immutable. The spring equinox does not have a fixed date and can occur on March 19, 20 or even 21 depending on the year. Moreover, in twenty years, in 2044, we will experience an equinox on March 19 for the first time since 1796. If this date should make an impression, it will not be an isolated event since we will find this date for the equinoxes of 2048, 2052 or even 2056. And this situation will continue to recur often until the end of the century, twenty times in total between 2044 and 2097.

On the other hand, to experience spring again on March 21, you will have to wait until 2102! Although this is the date we all have in mind to mark the start of spring, there will only have been two equinoxes on March 21 during the 21st century. On the other hand, there were 57 during the 20th century. The date of the start of spring therefore varies from year to year but also over the centuries!

To understand the variability of this date, we must look for the explanation in the rotation of the Earth around the Sun. Contrary to what one might imagine, the Earth does not take exactly 365 days to complete its orbit around the Sun. It takes just a little bit longer than that: 365.2422 days to be precise. To make up for this slight delay of about a quarter of a day, we have introduced the leap year system which occurs every four years, adding a day to the calendar at the end of February. However, this correction is not entirely accurate and it results in a slight shift at the time of the solstices and equinoxes which causes the length of the seasons to vary slightly.

This year, the spring equinox took place on March 20, 2024 at 4:06 a.m. and 21 seconds, according to the IMCCE. Marking the start of spring, it is the precise moment when the sun crosses the plane of the earth’s equator. Very concretely, it is the moment when the night lasts as long as the day, hence its name “equinox” which comes from the Latin “aequinoctium”, constructed with the terms “aequus” (equal) and “noctis” (night ).