The days are longer in summer and the nights are longer in winter. The beginning of spring and autumn mark the transitions when day and night are of equal length – or not?
March 20, 2023 is the meteorological beginning of spring, more precisely the evening of March 20, at exactly 10:24 p.m. Incidentally, this is also accompanied by the equinox. But what exactly does that actually mean? And why is the name, strictly speaking, incorrect?
The answer to that has to do with two days that are far more well-known: the summer and winter solstices. Mostly on December 21st, the winter solstice marks the moment when the days begin to get longer again. From the summer solstice (usually June 21st) the days get shorter again.
Equinox is little known
The equinox, also known as the equinox, is much less well known – at least under that name. It lies exactly between the summer and winter solstices and marks the period when day and night are exactly the same length. In general, however, the two days are known as the beginning of spring and autumn on the calendar.
This annual spectacle has to do with the fact that the earth’s axis is slightly inclined in relation to the earth’s orbit around the sun. This imbalance is responsible for the fact that we even notice when the earth has orbited the sun once. Because on its way around the bright star, the angle of the sun’s rays changes slightly and is sometimes more over the northern and sometimes more over the southern hemisphere. We experience summer and winter.
Equinoxes are the two times when the sun is directly above the equator. Then it shines exactly the same on the northern and southern hemispheres. And that’s exactly why day and night are exactly the same length all over the world – at least in theory. In practice, however, it is a bit more complicated.
In fact, at the equinox, the day is slightly longer than the night
This has something to do with the fact that the equinox is calculated from the center of the earth and the sun. However, the day already begins when the upper edge of the sun’s disk becomes visible above the horizon and it only ends when the last sun slit has disappeared.
Another aspect is the earth’s atmosphere, which breaks the light of the sun and thus makes the sun already visible on the horizon, although mathematically the horizon should actually still cover it. Accordingly, at the equinox, the day is a few minutes longer than the night.
If the day is actually exactly 12 hours long, it is called equilux, usually a few days before the beginning of spring and a few days after the beginning of autumn.
