Half year

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Sun position diagram for Bern : The path of the day's sun within a year. The upper half of the arc is the position of the sun in the summer half-year , the lower half that in the winter half-year

The summer half year is the time of year that lies between the astronomical beginning of spring and autumn . The other time of year is the winter half year . In the middle of each of the two semesters there is a solstice .

Half years and date

On the northern hemisphere of the earth that is the summer months the time between 20th March and 22. September , or between 21st March and 23. September , while on the southern hemisphere then the winter months there. In the northern winter half of the year the situation is exactly the opposite.

In the Gregorian calendar used today, the accumulating date deviation of one day is usually corrected every four years by a leap day . In the Julian calendar, on the other hand, which shows the length of the solar year less precisely, the equinoxes have already drifted forward by 13 days since the turn of the century . On a longer scale, variable earth orbit parameters also have an influence on the beginning of spring , mainly due to the precession of the earth's axis .

Half-years and climate

Because of Kepler's second law , the slightly elliptical orbit of the earth leads to a few days longer summer than winter in the northern hemisphere, in the southern hemisphere the opposite is accordingly the case. The point closest to the sun, the so-called perihelion , and thus the greatest speed on earth on its orbit around the sun, currently occurs at the beginning of January. Due to this slight asymmetry in the global distribution of solar radiation, the longer northern summers are theoretically a few percent warmer than those south of the earth's equator. Therefore the climate is z. B. at the 45th parallel in Argentina much rougher than at the corresponding degree north latitude in Europe , which corresponds roughly to a line along the cities of Bordeaux , Belgrade and Bucharest . In addition, there are regional influences such as the distribution of the continents and ocean currents. If in the cycle of perihelion the proximity to the sun has moved to June in a few thousand years, the situation is reversed. This may have an impact on the ice ages.

The connection between summer and the summer half-year becomes more and more obvious as the distance from the equator increases. The closer you get to the poles, the greater the difference in day lengths between the summer and winter months. In latitudes above the Arctic Circle , summer and summer half-year are almost congruent, the seasons spring and autumn are shortened to a minimum, in the direct vicinity of the poles the entire summer half-year is day and in the winter half-year night. The closer you get to the equator, the more similar the conditions of the summer and winter half-year are: In the tropics , the meteorological seasons are hardly pronounced and the days are around twelve hours long in summer and winter.

Economic aspects

In the economic use of solar energy , the above-mentioned influences make up a few percent. For example, well-designed thermal solar systems cover all the demand in the summer, whereas between October and March they only supply around 20% of the summer hot water. How far one therefore increases the size of the solar collectors requires an exact calculation - because the gain in summer energy can usually not be used.

The time of the time change between summer and normal time is based on the beginning and the end of the summer half-year and therefore took place on the last weekend of March or September. Since 1996, however, the normal time provision has been moved to the last weekend in October.

Web links

Wiktionary: semester  - explanations of meanings, word origins, synonyms, translations