A key astronomical event
The winter solstice is more than just a seasonal marker: it’s a fascinating astronomical phenomenon. It occurs when one of the Earth’s poles reaches its maximum inclination away from the Sun. This configuration, specific to the northern hemisphere in December, results from the 23.5° inclination of the earth’s axis relative to its orbital plane.
Origin of the name
The word “solstice” derives from the Latin “solstitium”, combining “sol” (sun) and “sistere” (to stop). This terminology refers to the illusion of a “stopped sun”, when its path in the sky appears to pause before reversing its direction. In many ancient cultures, the winter solstice was associated with the rebirth of the Sun and celebrated as a symbol of renewal.
Understanding how the solstice works
Winter solstice: day lengths around the world © The Weather Channel
The winter solstice occurs when the North Pole is tilted at its maximum away from the Sun. As a result, the duration of sunshine is at its minimum, with a day of only 8 hours in Paris and 7 hours in Lille. Meanwhile, the southern hemisphere is experiencing its summer solstice with endless days, like in Patagonia where the sun remains visible for up to 17 hours straight in Punta Arenas. In the northern hemisphere, certain areas such as Tromsø, Norway, or Barrow, Alaska, plunge into the polar night, a total darkness that can last several weeks. For example, in Tromsø, the polar night lasts from November 27 to January 15, providing a stark contrast to summers when the sun never sets, a phenomenon called the “midnight sun.” The latter is observable in places such as Svalbard, Norway, or Reykjavík, Iceland, where daylight persists for 24 consecutive hours around the summer solstice.
The precise moment of the solstice
The length of the days will increase again a few days after the solstice © The Weather Channel
The winter solstice is a bit like the “turnover” of the year, a key moment when the night reaches its peak and the days begin, very slowly, to take over. Contrary to what one might believe, it is not a whole day but a precise moment. In 2024, he will perform on Saturday December 21 at 9:20 a.m. UTC (i.e. 10:20 a.m. in France). This is when the Sun will be lowest in the sky at noon.
Now, a little useful clarification: even if the solstice marks the shortest day of the year, the days do not immediately get blatantly longer. For what ? It’s a story of celestial mechanics. The Earth, in orbit around the Sun, follows a slightly oval trajectory, and its axis is tilted. Result: the Sun continues to rise a little later until the beginning of January, while sunset begins to slowly lengthen from the end of December.
Clearly, from December 21, the total duration of light begins to increase, but this is not immediately visible. It’s only after Christmas that you really start to notice that the evenings are gaining a little light.
Differences between solstice and equinox
If the solstices mark the longest or shortest days of the year, the equinoxes symbolize the equality between day and night. These occur around March 20 and September 23, marking the start of spring and fall. Together, these events govern our calendar and influence our activities.
Consequences on seasons and weather
Although the winter solstice ushers in astronomical winter, meteorological winter begins on December 1. In France, the consequences are notable: the reduction in sunshine leads to lower temperatures and often harsh winter conditions. However, peak cold usually doesn’t arrive until mid-January. This phenomenon, called “thermal inertia”, is linked to the slow response of land and ocean masses to variations in sunlight.
A phenomenon measured with precision
At the time of the winter solstice, the length of the day is twice as short as that of the night © The Weather Channel
Historically, astronomers used instruments like sextants to observe the movement of the sun, while today the exact time of the solstice is calculated using modern instruments that combine direct observation and computer modeling. Organizations like NASA play a crucial role in providing accurate data on these events, reaffirming their scientific and cultural importance.
The winter solstice, this moment when night seems to prevail over day, actually brings hope. With him begins the slow march towards longer and brighter days. By understanding the subtleties of this astronomical event, we better understand the intricacy between terrestrial movements and their impact on our daily lives.
Winter solstice: day lengths on the European continent © The Weather Channel
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