It is not yet 6 p.m. that the Sun has already set. It’s winter. And as everyone knows, the days are short. As short as the nights are long in summer. Explanations.
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[EN VIDÉO] Kézako: do you know where the seasons come from? Each year has four seasons. In the northern hemisphere it is probably hot in summer and cold in winter. But where do these cyclical temperature variations come from? Unisciel and the University of Lille 1 reveal to us, with the Kézako program, the secrets of the earth’s seasons.
First of all, it seems necessary to bring a little clarification of language. Indeed, note that on our good old Earth, the days last 24 hours, and that whether one is in the northern hemisphere or in the southern hemisphere, on January 3 or August 25. ” In winter, some will object, it is still daylight much shorter than in summer! It’s undeniable “. ” Absoutely ! “, we will answer. We must therefore speak of shorter days and not shorter days. The nuance is subtle, but it exists.
This being said, let us now look at the cause of this phenomenon which has the gift of putting our mood strained on the days ofwinter. To understand, we will have to take a little height. And visualize the Earth-Sun couple in their space ballet. The Earth, everyone knows, turns on itself in 24 hours and that is what makes thealternating days and nights. The Earth, as everyone knows, also revolves around the Sun in one year.
Short days in winter: a question of inclination
So things could be very basic and binaries. If the axis of Earth rotation was kindly perpendicular to the ecliptic plane. But this one happens to be tilted. In fact, during the winter of the northern hemisphere, it is the southern hemisphere that is oriented most directly towards the Sun. It then benefits from maximum sunshine and longer days, while the northern hemisphere suffers from shorter days. And six months later, the situation is reversed.
In France – and in all the countries located at similar latitudes -, around the winter solstice, our days are struggling to reach 9 hours. But around the summer solstice, it’s the opposite: we enjoy up to 16 hours of sunshine. In countries on the equator, on the other hand, days and nights invariably last 12 hours. And the poles know alternately six months of the day and six months of night.
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