How do seasons arise? | EOS Science

We are already complaining about the weather. Too cold, too hot, too humid, too dry… It’s never good for some. However, we are lucky with our latitudes. It offers four seasons and a temperate climate, which is the source of the prosperity of our regions.

Around the equator the days are rather monotonous. The days are about the same length and the weather is about the same every day: warm with a dry season and a rainy season.

We live in a more diverse region, one with different day lengths and four seasons. But how does that happen? How do those chapters come?

The four seasons we know are the result of the tilt of the Earth’s axis. The Earth revolves around the Sun, but it is tilted at an angle of 23.5 degrees. As a result, the Earth is lit slightly differently every day of the year. This means that the sun is at a different height above the horizon every day of the year and that the length of each day is different. Diurnal differences are much greater at the poles than at the equator.

At the beginning of astronomical spring and astronomical autumn, the Sun is perpendicular to the equator. Day and night last about the same length. “About” because there is a difference of a few minutes due to the refraction of sunlight through the atmosphere and the fact that the sun is not a constant source, but that leads us very far here … Night and day are equal in length We are talking about the “equinox” for our astronomical spring, usually a day March 21, because fall is always around September 23, but it never happens on September 21, contrary to what some are taught in school.

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At the beginning of the astronomical summer, the Sun is perpendicular to the parallel Tropic of Cancer at 23.5 degrees north latitude. In areas above the Arctic Circle, above about 66 degrees, it does not darken during that time. The sun will remain above the horizon for several days.

Our astrological winter begins around December 21, when the Sun is perpendicular to the Tropic of Capricorn, at about 23.5 degrees south latitude. It will then be dark over the Arctic Circle for several days.

South of the equator, of course, the same reasoning applies, but there are seasons that are naturally reflected in the calendar year. In Australia they celebrate Christmas with a swimsuit.

The tilted axis of the earth provides not only different illumination and thus a difference between day and night, but also different heating of the earth. This explains the differences in temperatures between summer and winter. These differences are minimal at the equator, but greater in the north and south. Thus we get four seasons with different temperatures and different weather.

So far we have always talked about the astronomical seasons, the four seasons that are determined by the altitude of the Sun due to the tilt of the Earth. But there is also such a thing as “meteorological seasons” or “weather seasons”. This is a seasonal division established by climatologists for practical reasons. Calculating averages from the first day of the month to the last day of the month is easier and more statistically correct than having to take astronomy into account. The meteorological season always lasts three months and thus extends from the first day of the first month to the last day of the thirde Month. For example, the climatic spring with us runs from March 1 to May 31.

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