The worst is over: In the evening, it stays light again, at least for a few seconds. However, the shortest day of the year is not until 21. December. Even longer it takes to the latest sunrise. This only takes place on New Year’s morning.
Author: Felix Blumer
It’s always the same: It gets dark especially early in late November and the first days of December. This year the situation in the midlands was particularly depressing, it was especially gray due to fog and high fog. But the worst of the winter 2020/21 is already over. On Friday evening we experienced the earliest sunset of the year. In Zurich the sun sank by 16.35 o’clock below the horizon, in Basel, which lies further to the west, took place at 16.38 o’clock the sunset takes place. The last rays of the sun in Switzerland were at 16.49 o’clock in the city of Geneva.
Shortest day this year on 21. December
Although it will be light a little longer in the evening, the days will be longer until the 21st. December, the astronomical beginning of winter, still shorter. Then it is already two minutes and about 45 seconds longer light in the evening again, but this is compensated in the morning at the latest. Compared to today, the sun rises 8 minutes later on the shortest day. On 21. December, 8 hours and 27 minutes elapse between sunrise and sunset in Zurich. Due to the inserted leap day on 29. February, the astronomical beginning of winter takes place again on 21. December, last year it was still December 22.
Cause of the phenomenon: the equation of time
The reason that the earliest sunset and the shortest day do not fall on the same date is to be sought in the so-called equation of time. It expresses the difference between the theoretical daily solar maximum and the effective maximum and is today about 7 minutes. In plain language: In Zurich the sunset is actually at 12.26 noon. Then the sun reaches its theoretical maximum. However, because the earth orbits the sun on an elliptical path and the earth’s axis is inclined with respect to the orbit, the daily solar maximum or the daily noon varies. Especially in November, but also at the beginning of December, the sun reaches the noon point much too early. Today the sun’s peak is already at 12.19 o’clock, and accordingly both sunrise and sunset are premature.
On Christmas Day the equation of time is zero
On 25. December the sun is on time again and reaches at 12.26 o’clock the midday point. But it does not stay like this. Until 11. February, it is delayed more and more, and reaches the noon point only around 12.40 o’clock. For this reason we experience in Switzerland the latest sunrise also only on 1. January. As a result, in January and the beginning of February, it gets light for much longer in the evening, while in the morning it remains dark for what feels like an eternity.