Summer is the warmest of the four seasons in the subtropical, temperate, cold and arctic climates. Depending on whether it currently prevails in the northern or southern hemisphere, one speaks of northern or southern summer. The northern summer takes place simultaneously with the southern winter.
cause of summer
The seasons occur because the earth’s rotation does not occur in the plane of the orbit around the sun, but is inclined by 23.4 ° (see ecliptic skew). As a result, the north and south poles are alternately half a year in grazing sunlight, and the zenith of the sun alternates between the northern and southern tropics in the annual cycle.
duration of summer
Astronomically, summer begins with the summer solstice – the time when the sun is perpendicular to the tropic of its own half of the earth and the days are longest. The beginning of summer is
in the northern hemisphere on June 20, 21 or 22, or
in the southern hemisphere on December 21 or 22.
Then the days become shorter and the nights longer. The northern summer ends with the autumnal equinox on September 22 or 23 and the southern summer on March 20 or 21.
In the East Asian culture, which is shaped by the Chinese calendar, summer already begins when the sun is 45 ° before the solstice (May 5th, 6th or 7th), and ends when the sun is 45 ° behind (7th , August 8 or 9). The solstice is in the middle of summer. This quarter corresponds exactly to the time in which the sun is highest in the sky, that is, which has the potentially greatest radiance on the respective hemisphere.
Since the orbit of the earth around the sun is slightly elliptical, i. H. deviates from an exact circular path by 1.7 percent, the four seasons are not exactly the same length. The northern summer is slightly longer than the southern summer, since during the northern summer the earth is a little further away from the sun (Aphel on July 5) and its direction to the sun changes somewhat more slowly.
The phenological beginning of summer can deviate significantly from the astronomical one and is influenced not only by the land-sea distribution (maritime vs. continental climate) but also by initial large-scale weather conditions and various regional factors. A distinction is also made between early summer, midsummer and late summer.
Meteorologically, the months of June, July and August are assigned to the northern summer, and the months of December, January and February to the southern summer.
In Central Europe, the potential high point of summer with the highest temperatures is about three to six weeks after the summer solstice, i.e. between mid and late July, somewhat earlier with a more continental climate and a little later with a more maritime climate.
The so-called polar day prevails at the geographical poles for six months, in the arctic regions weeks of midnight sun and white nights.
In many cultures, customs and rites are associated with the beginning of summer, in Germany, for example, the Midsummer or Johannis fire. Otherwise, summer is also the season of increased joie de vivre. This is particularly the case for stays and outdoor activities caused by the higher temperatures, e.g. B. on bathing lakes, as well as on hormones released by solar radiation.