Friday marks the official start of spring, which is taken when the days become longer than the nights.
On the day equinox falls, the plane of the Earth's equator passes the exact centre of the Sun, meaning the planet is neither tilted towards or away from the Sun.
So from Friday, the nothern hemisphere will begin to tilt towards the Sun, meaning we can expect warmer weather. Time to start dusting off your diet books and getting that beach body you promise yourself every year ahead of summer, which officially starts on June 21.
Clocks don't go forward for another few days –British Summer Time, which robs us of an hour in bed, officially starts on March 29.
This is the astronomical season change. The meteorological definition used by the Met Office – which is based on the annual temperature cycle – has spring arriving three weeks earlier, which means it began on March 1.
Meteorological spring will run until May 31, when summer begins.
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