This year, the winter solstice in the northern hemisphere will occur on December 21 at 9:21 am GMT (10:21 am Madrid, 3:21 am Mexico City), thus beginning the season. For those who live in the northern hemisphere, December 21 will be the day with the fewest hours of daylight in all of 2024. Afterwards, the days will again be longer and the nights shorter, until the spring equinoxwhen the hours of light and darkness will be equal. In the southern hemisphere, however, December 21 will mark the beginning of summer and will correspond to the day with the most hours of light of the entire year (it will occur at 6:21 am in Buenos Aires and 4:00 am in Bogotá).
What does the date of the winter solstice depend on?
The summer and winter solstices (like the spring and autumn equinoxes) do not fall on the same day every year. In 2023, for example, the winter season began in our hemisphere not on December 21, but on December 22. In fact, the solstices and equinoxes correspond to precise events that occur around the same dates each year, but not exactly.
The day of the winter solstice, specifically, coincides with the day on which the Sun reaches the lowest point of its apparent motion. In other words, if we photographed the Sun every day of the year at the same time from the same point on Earth, the day of the winter solstice would be the day when the Sun is at its lowest point in the sky, i.e. , closer to the horizon. The opposite is true for the summer solstice.
The equinoxes, for their part, occur at the two times of the year when the Sun’s rays are exactly perpendicular to the Earth’s axis. They correspond, by the way, to the only two times of the year in which the two terrestrial hemispheres receive the same hours of light from the Sun.
Equinoxes and solsticesDivad – Own work, public domain / Wikimedia CC0 Public Domain
The fault lies with the earth’s axis
The alternation of the seasons is due to the fact that The axis of the Earth is not perpendicular to the plane of the eclipticthat is, to the plane on which the Earth’s orbit is located. The Earth’s axis is tilted 23.5° and this means that, during the revolution around the Sun, the two terrestrial hemispheres do not always receive the same number of hours of light.
If, on the other hand, the axis of the Earth were exactly perpendicular to the plane on which the Earth moves in its revolution around the Sun, There would be no seasons. In that case, if we photographed the Sun every day of the year at the same time and from the same point on Earth, we would always see it at the same height above the horizon.
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