This year winter starts on Friday December 21st at hours 10:20 in the morning Italian, date and time in which the winter solstice. This astronomical event and symbolic moment for many cultures does not always fall on the same day but usually occurs between December 20th and 23rd and marks thebeginning of the winter season in the northern hemisphere. The day of the winter solstice is the one with the shortest day of the year (which is not the day of Saint Lucia) and the longest night of the year. Let’s see what happens to the relationship between Earth and Sun to understand why this anniversary always falls on these days of the year: essentially, the phenomenon is due to the inclination of the Earth’s axis, which causes the inclination of the sun’s rays to vary during the year: at the time of the December solstice, the inclination is maximum in the northern hemisphere and minimum in the southern hemisphere.
What happens during the winter solstice
The winter solstice marks thestart official ofastronomical winter. As with the equinoxes (spring and autumn), they occur every year two solstices: once a year in June (which in the Northern Hemisphere is summer solstice) and one in December (the winter solstice in the Northern Hemisphere). But what happens on this day from a scientific point of view? The Earth, in addition to rotating daily around its axis (the imaginary line that connects the North Pole to the South Pole) also rotates around the Sun. The fact that the Earth’s axis is inclined by 23°27′ with respect to the plane of the Earth’s orbit is the cause of the alternation of seasons.
What happens during the December solstice is that solar rays reach the minimum inclination with respect to the horizon in the northern hemisphere and the greatest inclination in the Southern Hemisphere. In particular, in the December solstice the Sun reaches the zenith along the Tropic of Capricorn in the southern hemisphere (the light falls perpendicular to the ground and objects do not send further), while above the Arctic Circle the Sun fails to rise above the horizon.
If the Earth’s axis were perpendicular to the plane of the Earth’s orbit the Sun would be at the zenith everywhere and on every day of the year, therefore there would be neither solstices nor equinoxes nor seasons, and the so-called circle of enlightenment (i.e. the part of the Earth illuminated by the Sun) would always extend from the North Pole to the South Pole.
If we took a photograph of the Sun at the same time every day for a year and in the same location, we would notice that the apparent motion of the Sun it rises and falls during the months, marking seasonal paths, following a sort of inclined “8” which takes the name of analemma. The winter solstice represents the lower end along the axis of the analemma. The summer solstice represents the opposite extreme and the equinoxes are approximately at the “choke” point of the analemma.
When does the winter solstice fall 2024: the date and time
Although the solstice is often thought of as a full day, it actually lasts only one moment: in 2024 the winter solstice will fall on December 21st at 10.20am in the morning (Italian time). The date of the winter solstice is not actually always the same, but it can fall within a window of time that varies from 20 to 23 December due to an imperfect correspondence between the solar year and the calendar year.
THE’anno solar (i.e. the time that the Sun takes to complete its apparent cyclical movement in the sky during the Earth’s orbit) lasts a few hours longer thancalendar year Of 365 daysthe on which our calendar is based: this is why the winter and summer solstices “slip” by approximately 5 hours and 48 minutes from year to year. This delay accumulates, but is then partially canceled out by leap years, which introduce an extra day every 4 years.
Because it is the shortest day and the longest night of the year
They call it the shortest day of the year (or rather, the shortest day) for a reason: the winter solstice is the day with the fewer hours of light of the northern hemisphere. This definition derives from the fact that the Sun travels the shortest route across the sky: we will therefore have less daylight and a longer night. From this moment on, the hours of light will tend to increase until the summer solstice, when they will begin to reduce again.
Contrary to what we sometimes hear, the shortest day (or the longest night) is therefore not that of Saint LuciaDecember 13th, but it is always – by definition – the day of the winter solstice.
Meaning and origins
This fact was already known in ancient times withthe Latin term solstitium which roughly means “stopping of the Sun”. As is clear by observing the analemma, during the solstices the Sun varies its position in the sky only slightly, so much so that seem still.
Depending on the time of year we are in, this path varies for us observers: in summer the Sun is at midday will be more high in the sky, in winter more Bassreaching its maximum peak during the summer solstice and its minimum during the winter solstice. Not only that: if we look at our own shadow at noon, on the day of the winter solstice it will reach its maximum length, while on the summer solstice its minimum length.
