March 1, 20 or 21: when does spring really start?

One says it’s spring from March 1, the other says March 19 or 20, and many calendars say the 21st. Hugely confusing. Yet there is an explanation for all this confusion. There are 3 ways to look at the start of a season. And they all have a different start date.

Meteorological

According to the KNMI, March 1 is the date on which spring begins from a climatic point of view. Weather experts therefore assume that spring runs from March 1 to May 30, so exactly 3 months. This is mainly a practical decision made in 1870, when a German elector decided to use 3 calendar months per season for the sake of convenience.

Astronomical

The astronomical view of the seasons makes the start of spring depend on the position of the sun. Every 3 months, around the 21st of that month, the sun will be on the equator or the tropic. It will be light almost everywhere on Earth for the same amount of time. This ushers in the new season. Yet there is not exactly one year between the springs. That’s because it doesn’t take exactly 365 days for the sun to return to the equator or tropic. It takes 365 days, 5 hours, 48 ​​minutes and more than 45 seconds for the earth to orbit the sun. So there is no fixed date on which spring starts, because the start of spring always moves forward by 5 hours, 48 ​​minutes and 45 seconds. To ensure that the start of the seasons does not move too much, the leap year has been introduced. With that one extra day once every 4 years, the shift is corrected again. This causes the astronomical spring to start on March 20 this year.

Officially

For convenience, an official date has also been set for spring to begin. This is March 21, because astronomical spring always starts around that date.

Source: KNMIquest

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