Welcome spring: in 2025 the summer begins Thursday 20 March precisely at 10:01 Italian. Well yes: the seasons begin with a specific time, and spring is no exception. At 10:01 on 20 March 20225 thespring equinoxone of the two “key moments” that affect our planet during its orbit around the sun. In particular, the spring equinox is one of the two moments in which The day is equally divided into 12 hours of light and 12 hours of darkness Everywhere in the world and falls between 19 and 21 March, officially starting spring in the northern hemisphere and autumn in the southern hemisphere. The other of these moments is the autumn equinox that falls between 21 and 24 September and this year the September 22nd At 19:19 Italian, marking the official beginning of autumn in the boreal hemisphere and spring in the southern hemisphere. A few days after the spring equinox there will be another annual appointment connected to spring: the return of the legal hour scheduled in Italy on March 30, 2025 at 2:00 am.
What does the spring equinox from an astronomical point of view mean
From an astronomical point of view, technically the two equinoxes are the two moments in which the Sunin its apparent annual motion in the sky, crosses the celestial equatorthat is, the projection of the terrestrial equator in the celestial sphere. In fact, remember that the rotation axis of the earth is not perpendicular to the plan of its orbit, but inclined 23 ° 27 ‘: this also makes the plane of the celestial equator compared to the terrestrial orbital plane, which is also – approximately – the plan in which the sun performs its apparent motion in the sky. In the March equinox, the sun “climbs” the celestial equator from below to above the equator itself in the northern hemisphere, while it appears to go down under the celestial equator in the southern hemisphere. The opposite in the autumn equinox: the sun goes down under the celestial equator in the northern hemisphere and goes up to it in the southern hemisphere.
From a geometric point of view, in the moment of the equinox The management of the Earth axis has no component towards the sun Nor in the opposite direction: it focuses “perpendicularly” to our star. It is this particular geometric arrangement that ensures that the day lasts 12 hours everywhere on the planet. A consequence of this fact is that, on the day of the equinox, Solar rays are perpendicular to the terrestrial equator And therefore the sun is located at Zenit at every point of the equator: here the objects do not project shadows in the south of the equinox!
Another consequence of the arrangement of the Earth’s axis at the time of the equinox is the fact that the sun that day It is exactly east and sets exactly to the west. Contrary to what you think, this does not always happen but only in the two days of the spring and autumn equinox.
In addition, the equinoxes are the two days in which the terminator (the imaginary line that separates the illuminated part of our planet from the dark one) passes through the North Pole and the South Pole. In the spring equinox, the sun then returns to peek at the North Pole and instead disappears from the sight to the South Pole.
All this, we remember, is due to the fact that The terrestrial axis is inclined Compared to the orbital plan of the earth: if it were not so, every day of the year the day would have a duration 12 hours everywhere in the world.
When and what time starts spring 2025
All this should help us understand why the spring equinox is not associated with a generic date but with a precise moment. And it should also help us understand why It is precisely the Equinox of March that marks the beginning of spring: This is in fact the moment that the earth-Sole geometry makes sure that the day, after starting to stretch starting from the winter solstice, begins to overcome the night in duration.
This year the spring equinox falls the March 20 at 10:01 am In Italy, thus officially giving way to the summer.
Because the spring equinox always changes given
A commonplace to dispel is the fact that The seasons begin on the 21st of the month (i.e. spring on March 21, summer on June 21, autumn on September 21 and winter on December 21). As we have seen, the exact moment of the beginning of a season depends on astronomical considerations linked to motorcycle of the earth around the sun. If the duration of one year was Exactly equal to a whole multiple lasting one day, the seasons would follow a perfect cycle and every year they would always begin on the same day. But we know it’s not like that: if a civil year hard Exactly 365 days For practical reasons, a calendar instead it lasts slightly more, to be precise 365.25 days, or 365 days, 5 hours and 48 minutes about.
This 1/4 -day waste is the reason why we add one day to the calendar every four years – on February 29 – with the bisastile years, but it is also the reason why The dates of solstices and equinoxes I can vary within an interval of a few days. The spring equinox is actually “stable” to March 20 for several years: in the last quarter of a century it has always fallen on March 20, except in the 2003 and in 2007 When he fell on March 21st.
This goes for the “official” seasons, that is, the astronomical seasons. Then there are the Meteorological seasonsused precisely in the meteorological field, which always begin on the 1st of the month (therefore March 1st, June 1, September 1 and December 1).
