Winter is getting closer. If meteorological winter arrived on December 1, calendar winter will begin this Saturday, December 21, the day of the winter solstice. This phenomenon corresponds to the shortest day of the year and therefore the longest night of the year.
If this short day may seem depressing for some, they can console themselves by taking into account that from this date, the days will become longer and longer each day until the next summer solstice, that is- i.e. June 21, 2024.
On the other hand, the most observant will have noticed that the sun has been setting later and later since December 11, but the days still continue to shorten. Indeed, the sun will also continue to rise later each day until December 31, and it is therefore only on December 21 that the days will be longer and longer.
Although it marks the change of season on our calendar and the shortest day, the winter solstice is actually a much more complex astronomical phenomenon than that. It occurs when, as it rotates, the Earth’s axis orients the North Pole at its furthest point from the sun, the complete opposite of the summer solstice.
According to the Institute of Celestial Mechanics and Ephemeris Calculation of the Paris Observatory (IMCCE), “the winter solstice corresponds to the moment when the apparent geocentric longitude of the Sun is equal to 270°”.
This phenomenon is explained by “the inclination of the earth’s axis, which remains oriented in the same direction throughout the year, while the earth orbits around the sun”, specifies the Weather Channel. Each year, during its trajectory around the Sun, the Earth occupies four positions which mark the beginning of the seasons: the equinoxes, for spring and autumn, and the solstices, for summer and winter.
Each year, the winter solstice does not occur on the same date but takes place on December 21 or 22. The date changes because our calendar year lasts 365 days three years out of four, while the duration of the Earth’s rotation around the Sun is 365 days, 5 hours and 48 minutes. This is why we have a year of 366 days every four years, a leap year, to compensate for the days missing from our calendar compared to the actual number of days.
