Many people feel that the days get longer more quickly in March. This is no imagination; the daylight hours increase more than in any other month of the year. But what is the reason for this?
Around Christmas, it feels dark around the clock in our latitudes. Only in January does the situation improve, until the days seem to get longer and more quickly in February and March. An impression that is not deceiving: the length of daylight grows faster in March than at any other time of the year.
“The different increase in day length is due to the inclination of the Earth’s axis compared to the orbital plane around the sun,” says Janine Fohlmeister of the Leibniz Institute for Astrophysics Potsdam ntv.de. The Earth’s axis is tilted by 23.5 degrees and always points in the same direction. That’s why the length of the day in summer is much longer than in winter and constantly changes throughout the year.
But why do the days not get longer evenly from winter to summer? Mathematics provides the answer: the number of daylight hours at a given location on Earth is a periodic function of time. And that has consequences: “The course of the development in day length corresponds to a sine curve,” says Fohlmeister. Everyone knows this uniform wave from math class. It has a fixed high and low points.
When orbiting the sun, summer and winter solstice correspond to the highest and lowest points of the sine curve. “Around these points in time, the lengths of the day change only slowly,” Fohlmeister says. That’s because the slope of the sine curve is then very flat in each case.
Peak around March 20
At the beginning of the year, the rise of the sine curve becomes steeper and steeper, which means a faster increase in the day length. It is most dramatic at the equinox around March 20. Then the pace slows down again, and the day length goes downhill from the summer solstice on June 22. However, hardly anyone is likely to complain about this at that time – with almost 17 hours of brightness per day.
But you can already guess: While the sine curve in spring puts you in a good mood, it also has its dark side. Because in late summer, the loss of brightness also noticeably picks up speed. Around the autumnal equinox on September 23, the days became shorter as rapidly as they became longer in the spring. After that, the whole thing slows down again. But by the winter solstice on December 22, only about seven and a half hours of daylight remained.
By the way: If all this is too exciting for you with the days getting longer and shorter, there is a solution. At the equator, the length of the day changes only minimally throughout the year. There you can always look forward to more than 12 hours of daylight. Sunrise is always between 6:15 and 6:30 in the morning. But let’s be honest: That’s a bit boring in the long run.
- Source: ntv.de/picture: Image by Jill Wellington from Pixabay
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