The December 21, 2025at hours 4.03pm Italians, the winter solsticewhich will officially begin the winter season in the Northern Hemisphere. Contrary to what you think, the change of season does not happen over the course of an entire day, but falls at a specific timeand does not occur on the same day every year, but varies between December 20th and 23rd.
The winter solstice corresponds to the day with the shortest day of the year and the longest night of the year, with the Sun which reaches it zenith along the Tropic of Capricorn. From one point of view symbolichowever, represents a rebirth after the end of autumn.
Unlike the famous saying, therefore, “the shortest day there is” is not that of Saint Luciawhich occurs on December 13th.
How the winter solstice works from an astronomical point of view
The winter solstice marks the official start of astronomical winter in the northern hemisphere. Just like the equinoxes (spring and autumn), they occur every year two solstices: the first a Junewhich decrees the beginning of summer, and one a Decemberwhich kicks off the winter season.
But how does all this work from an astronomical point of view? The reason is due to the Earth’s axis, which is inclined with respect to the plane on which the Earth orbits: specifically, theinclination of the earth’s axis is 23°27′. And, as our planet moves along its orbit around the Sun, this tilt means that over the course of the year changes Also the height of the Sun in the sky and consequently the duration of Of: it’s the same reason why the seasons alternate on our planet.
What happens during the winter solstice is that the sun’s rays reach the minimum inclination relative to the horizon in the Northern Hemisphere and the maximum inclination in the Southern Hemisphere. In particular, on the December solstice the Sun reaches its zenith along the Tropic of Capricorn in the southern hemisphere, while above the Arctic Circle the Sun is unable to rise above the horizon.
In fact, if the Earth’s axis were perpendicular to the plane of the Earth’s orbit, then the Sun would be at the zenith everywhere and on every day of the year: consequently, there would be neither solstices nor equinoxes nor seasons, with the so-called circle of enlightenment (i.e. the part of the Earth illuminated by the Sun) which would always extend from the North Pole to the South Pole.
When does the winter solstice 2025 occur: date and time
In 2025 the winter solstice will fall on December 21st at 4.03pm (Italian time). The date of the winter solstice is actually not always the same, but varies slightly from year to year and can fall in a time window ranging from December 20th to 23rd, due to an imperfect correspondence between the solar year and the civil year.
This is due to the fact that the motion of the Earth around the Sun it doesn’t last exactly 365 days but about 365.25 days: this gap between the duration of the solar year and that of the Gregorian calendar varies the moment in which the Sun reaches these four “critical” moments in its apparent motion in the sky. This delay accumulates, but is then partially canceled out by leap yearswhich introduce an extra day every 4 years.
Why it is the shortest day of the year: the meaning
The winter solstice is often defined as the “shortest day of the year”: in reality, it is the say shorter of the year, being the day with the fewer hours of light of the northern hemisphere. In the southern hemisphere, however, it is the day with the most hours of light of the year.
This comes from the fact that the Sun travels the shortest path across the sky: we will therefore have fewer hours of daylight and a longer night. From this moment on, the hours of light will tend to gradually increase until the summer solstice, when they will begin to reduce again.
In short, contrary to what the nursery rhyme says, «the shortest day there is” it is not the one in Santa Lucia (which falls on December 13th), but it is always – by definition – the day of the winter solstice.
