Spring begins: Friday 20 March 2025 at 3.46pm Italians fallsspring equinoxthe moment in which the Sun crosses the celestial equator thus officially beginning the summer. The spring equinox is one of the two moments of the year – together with the autumn equinox – in which the Sun “crosses” the equator: in March it “enters” the northern hemisphere, while in September it enters the southern hemisphere. As a first approximation, the days of the equinox are those in which the day is equally divided into 12 hours of light and 12 hours of dark everywhere in the world: in reality, however, this happens on the day ofequilight which falls a little before the equinox in our hemisphere and a little after in the southern hemisphere.
The spring equinox falls between March 19th and 21st, but since 2008 it has arrived on March 20th: it will not fall on March 21st until 2102. The autumn equinox can fall between September 21st and 24th and this year it will arrive September 23 at 2:04 am Italian time. A few days after the spring equinox there will be another annual event connected to spring: the return of summer time expected in Italy on March 29, 2026 to 2:00 am.
What is the spring equinox from an astronomical point of view: when and what time does it fall in 2026
From an astronomical point of view, technically the two equinoxes are the two moments when the Sunin its apparent annual motion in the sky, crosses the celestial equatorthat is, the projection of the Earth’s equator onto the celestial sphere. In fact, let us remember that the Earth’s rotation axis is not perpendicular to the plane of its orbit, but inclined of 23°27′: this also makes the plane of the celestial equator inclined with respect to the Earth’s orbital plane, which is also – approximately – the plane in which the Sun carries out its apparent motion in the sky. On the March equinox the Sun “crosses” the celestial equator from below to above the equator itself in the northern hemisphere, while it appears to descend below the celestial equator in the southern hemisphere. The opposite is the case at the autumnal equinox: the Sun descends below the celestial equator in the Northern Hemisphere and rises above it in the Southern Hemisphere.
From a geometric point of view, at the moment of the equinox the direction of the Earth’s axis has no component towards the Sun nor in the opposite direction: it points “perpendicular” to our star. It is this particular geometric arrangement that makes the day last 12 hours everywhere on the planet. A consequence of this fact is that, on the day of the equinox, the sun’s rays are perpendicular to the Earth’s equator and therefore the Sun is at the zenith at every point of the equator: here the objects do not cast shadows at midday of the equinox!
Another consequence of the arrangement of the Earth’s axis at the moment of the equinox is the fact that on that day the Sun it rises exactly in the east and sets exactly in the west. Contrary to popular belief, this does not always happen but only on the two days of the spring and autumn equinox.
Additionally, the equinoxes are the two days when 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. At the spring equinox the Sun then appears again at the North Pole and instead disappears from view at the South Pole.
This year the spring equinox falls on March 21st at 3.46pm (Italian time).
The day doesn’t last Exactly 12 hours on the day of the equinox
It is a common notion that on equinox days the day is divided into 12 hours of light and 12 hours of dark. It’s not wrong, but it’s not either Exactly True. It is with excellent approximation: in our latitudes, for example, the difference is approximately 10 minuteswhich isn’t much in the space of 24 hours. But if we want to be very precise, the day in which day and night have exactly the same duration (called equilight) falls a little earlier or a little later than the equinox, depending on where we are in the world. In Italy, for example, the spring equiluce fell on March 17therefore 3 days before the equinox.
There are two reasons for this difference. The first, and most important, is that the day begins when the solar disk begins to emerge from the horizon and ends when it finishes dipping into the horizon. Taking into account the fact that the Sun takes a few minutes to completely cross the horizonthis means that the day is a little longer than 12 hours on the day of the spring equinox.
The second reason, of lesser importance and more technical, is that sunlight is refracted slightly by the Earth’s atmosphere, making the Sun appear a little higher in the sky than where it actually is.
Because this year it doesn’t fall on March 21st either
A cliché to dispel is the fact that the seasons begin on the 21st of the month (i.e. spring on March 21st, summer on June 21st, autumn on September 21st and winter on December 21st). As we have seen, the exact moment of the start of a season depends on astronomical considerations related to the motion of the Earth around the Sun. If the duration was one year Exactly equal to an integer multiple of the duration of a day, the seasons would follow a perfect cycle and every year would always begin on the same day. But we know that this is not the case: if a calendar year hard 365 days exactly for practical reasons, a calendar year however, it lasts slightly longer, to be precise 365.25 days, that is 365 days, 5 hours and 48 minutes about.
This gap of 1/4 day per year is why every four years we add a day to the calendar – February 29th – with leap years, but it is also why the dates of solstices and equinoxes may vary within a period of a few days. The spring equinox has actually been “stable” on March 20th for several years: the last time it fell on March 21st was in 2007 and the next one will be in 2102; we will have to wait for the solar and calendar years to “realign” (with the complicity of leap years) in order to have the equinox on the day tradition dictates. To have a spring equinox on March 19th, however, we will have to wait until 2044.
Rites and celebrations of the first day of spring
Since ancient times, the spring equinox has been universally associated – at least in the northern hemisphere – with the awakening of nature and therefore, indirectly, with the idea of rebirth.
Let’s think about ours Easterwhich has a clear meaning of rebirth and its date is calculated starting from the spring equinox. Or at Shunbun in Japan, which is celebrated in early spring by visiting the graves of deceased family members. The first day of spring is a national holiday in Egypt, probably in continuity with the tradition of the holiday Sham el Nessim which dates back to the time of the ancient Egyptians and was associated with Osiris, a deity linked to fertility. In India and Nepal it is then celebrated Holithe festival of colors which falls at the very beginning of spring and is associated with the victory of Good over Evil.
