DefinitionThe seasons constitute one of divisions of the year, generally based on the annual changes of weather time. They correspond, according to the terrestrial geographical areas and the traditions, at the periods which separate the passage from the Ground at certain points of its orbit or, reciprocally, of the Sun at certain points of the celestial Sphère, and which the Celestial mechanics indicates by the equinox S and the Solstice S.
Thus, in the zones of moderate Climate, the astronomical seasons correspond coarsely to four phases of evolution of the climate in the Année: Spring, be, Fall, Winter. In the zones of tropical Climate, one also speaks about Saisons but in the direction of Rain season and Saison dries.
Climatic variations and celestial mechanicsThe seasonal climatic variations are created by a double factor: on the one hand the Revolution of the Ground around the Sun, and on the other hand the slope of the North-South axis of rotation day laborer of the Earth compared to the plan of sound Orbit around the Sun (ecliptic).
According to the position of the Earth compared to the Sun its orbit, the zone which receives the rays of the perpendicular Sun of way thus modifies. The more the rays arrive close to the perpendicular (i.e. the closer the Sun is to the zenith), the more it makes hot.
For a terrestrial observer, throughout the year, the Sun, although fixes, seems to oscillate around the equator, so that it lights perpendicularly and successively, as the tabelle one indicates it located below:
the equator, about the 20 or March 21st, with the equinox of spring (northern hemisphere) or autumn (southern hemisphere);
- the tropic of North, about the 20 or June 21st, with the Solstice of summer (northern hemisphere) or winter (southern hemisphere);
- the equator, again, about the 22 or September 23rd, with the spring or autumnal equinox (northern hemisphere) (southern hemisphere);
- the tropic of the South, about the 21 or December 22nd, with the summer or winter solstice (northern hemisphere) (southern hemisphere).
The names of the seasons and the variations climatic are thus reversed in the two hemispheres.
According to a very current generally accepted idea, the seasons would depend on the distance Ground-Sun, the ground being closer to the sun in summer than in winter. This idea is without the least base, because she explains neither the variations of the duration of the day, nor the inversion of the seasons between the hemispheres southern and boreal. The average distance Ground-Sun is of 150 million km with an annual variation of approximately 2,5 million km (either 1,6%). Currently, the Earth is with closest to the Sun (Périhélie) about on January 3rd, either in the neighborhoods of the Solstice of winter (hemisphere northern) and with further (Aphélie) about on July 3rd, or shortly after the Solstice of summer (northern hemisphere). It was the reverse 12.900 years ago, according to the cycle of precession of the equinoxes. From the variation of the distance Ground-Sun, the seasons should have a larger contrast in the Southern hemisphere compared to the northern Hemisphere. Only, very often of the local effects (proximity of the oceans, winds dominant…) come to contradict this forecast. This variation has another consequence, because the ground moves more quickly around the Sun when it is more close (in a general way, plus a body in orbit is " bas" , more it turns quickly; Venus, nearer to the Sun than the Earth, makes the turn in 9 months of it). So the season on which fall on January 3rd is shortest. A simple calculation starting from the table below shows it: 92 days for spring, 94 days for the summer, 90 days for the autumn, 89 days for the winter. It is true for the seasons of the northern hemisphere, whereas for the south, it is the summer which is the shortest season and the winter longest. The effect of this phenomenon on the differences in climate between the two hemisphere is an interesting question, but whose author of these lines does not have the answer.
Another interesting phenomenon: the difference in total temperature , which would be of approximately 4°C between the perihelion and the aphelion with a uniform surface, in fact is surprisingly reversed. It is lorque the Earth is closest to the Sun which it is the least hot! This due mainly to the imbalance of the ground ratio/ocean: the southern hemisphere being with 90% sailor. The total temperature integrated of the Earth would be thus higher with the aphelion of 2,3°C.
Astronomical season and calendarIn the European tradition, the beginning of the seasons is defined by the solstices and the equinoxes in the northern Hemisphere: the Printemps begins with the equinox from March (towards the March 21st), the be with the Solstice of June (towards the June 22nd), the Automne with the equinox of September (towards the September 23rd), the Hiver with the Solstice of December (towards the 21 December). In this tradition, the longest day and having the strongest incidence of the rays of the sun is regarded as the beginning summer. This fact takes account of a reality: April 21st, it can still freeze and on August 23rd, there are still heat waves: however the insolation of these two days is almost equal. In France, the hottest day on average is towards the coldest on July 28th and about on January 27th. It is the thermal Inertia which induces a delay between variation of the Sun and temperature. If one compares the Earth with a pan on a gazinière, the summer solstice (June 21st in France or December 21st in Australia) corresponds to a relatively hot pan on a flame regulated to the maximum. If one lowers just a little the flame (what corresponds to the progressive reduction in the duration of the sunning during the summer months) the temperature nevertheless continues to increase.
It goes from there differently in the East. The solstices and the equinoxes are regarded as the middle of the seasons. Thus, on June 21st being the middle of the summer and not the beginning, the summer thus starts about on May 6th, the autumn about on August 6th, the winter about on November 6th, spring about on February 6th (which marks the period of the Chinese new year). This is perhaps the consequence of a less thermal delay in continental Climat than in oceanic Climat, where water has a strong effect of thermal plug.
This explanation seems all the more logical as Russia admits an intermediate definition of the seasons, halfway between the European design and the Chinese design: spring: March, be: June; autumn: September; winter: December.
The structure of the calendar year in four seasons does not apply everywhere; it is characteristic of the areas of the moderate zone . On the other hand, between the two tropics for example, the Sun is always sufficiently close to the perpendicular so that the difference in temperature between summer and winter is not very marked. There are then often only two “ saisons ” (with the climatic direction): a Rain season and a Saison dry, and the climate is there tropical (or sometimes desert, according to the geographical location).
- In the moderate zone , one speaks about full seasons (summers, winters), and about semi-seasons (spring, autumn).
- a " commercial of 4 saisons" is a person who sells in the streets on a carriole, fruit and vegetables of season.
- - cabbages and oranges in winter,
- - salads and cherries in spring,
- - eggplants and melons in summer,
- - pumpkins and medlars in autumn.
- - salads and cherries in spring,
Festivals and celebrationsVery schematically in the various boreal traditions, since millenia, each springtide is marked by a festival:
- Easter for spring,
- the Midsummer's Day for the summer,
- Halloween, Oktoberfest or the Saint-Vincent for the autumn,
- Christmas for the winter.
These festivals had, in the rural world, an enormous importance as well social as religious. Nowadays, the stress is rather laid on their festive and/or commercial aspect.
See tooTheater season
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