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A season is one of the major divisions of the year. Typically, the year is divided into four seasons: spring, summer, autumn (fall), and winter. Some cultures may have a different number of seasons; for instance, some indigenous peoples in Australia's Northern Territory use six seasons.
In tropical and even subtropical regions it is more common to speak of the rainy (or wet, or monsoonA monsoon is a periodic wind, especially in the Indian Ocean and southern Asia. The word is also used to label the season in which this wind blows southwest in India and adjacent areas that is characterized by very heavy rainfall, and specifically the rai) season versus the dry season , as the amount of precipitationIn meteorology, precipitation is any kind of water that falls from the sky as part of the weather. This includes snow, rain, sleet, freezing rain, hail, and virga. Precipitation is a major part of the hydrologic cycle, and is responsible for depositing mo may vary more drastically than the average temperature.
The seasons are caused ultimately by the fact that the Earth's axisAxis has several uses: In mathematics, an axis is a straight line around which a geometric figure can be rotated. An axis of symmetry is a line with respect to which a body can be symmetrical. The term is also applied for the axis of a graph; the horizont is not perpendicularAxial tilt is an astronomical term regarding the inclination angle of a planet's rotation axis in relation to its orbital plane. It is also called obliquity . A planet whose rotation axis were perpendicular to the orbital plane would have an axial tilt of to its orbital planeThe orbital plane is an astronomical concept. It is the geometrical plane in which the orbit of a planet or other body is embedded.; it deviates by an angle of approximately 23.5 degrees of arcThis article describes "degree" as a unit of angle. For alternative meanings, see Degree (disambiguation). A degree of arc usually symbolized by the symbol °, is a measurement of plane angles, or of a location along a great circle of a sphere (such as the. Thus, at any given time during the summer or winter, one part of the planet is more directly exposed to the rays of the SunThe Sun (also called Sol is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally capt (see Fig. 1). This exposure alternates as the Earth revolves in its orbit. At any given time, regardless of season, the northern and southern hemispheres experience opposite seasons (see Fig. 2 and Seasonality table).
In most parts of the world, seasons are marked by changes in the amount of sunlight, which in turn often cause cycles of dormancy in plants and hibernation in animals. In the tropics, there is no noticeable change in the amount of sunlight, but there are still fluctuations in rainfall, producing a similar alternation between fertile and infertile times of the year. The concept of seasonality originated from these changes long before its celestial cause became known.
These fluctuations are more pronounced at higher latitudes. The Equator does not have any noticeable fluctuation at all, while the North Pole and South Pole have extreme fluctuations.
Seasonal weather fluctuations also depend on factors such as proximity to oceans or other large bodies of water, currents in those oceans, El Niņo/ENSO and other oceanic cycles, and prevailing winds.
For example, the South Pole is in the middle of the continent of Antarctica, and therefore a considerable distance from the moderating influence of the southern oceans. The North Pole is in the Arctic Ocean, and thus its temperature extremes are buffered by the presence of all that water. The result is that the South Pole is consistently colder during the southern winter than the North Pole during the northern winter.
The cycle of seasons in the polar and temperate zones of one hemisphere is opposite to that in the other. When it is summer in the Northern hemisphere, it is winter in the Southern hemisphere, and vice versa, and when it is spring in the Northern hemisphere it is autumn in the Southern hemisphere, and vice versa.
Curiously, a study of temperature records over the past 300 years (David Thompson, SCIENCE, April 1995) shows that the climatic seasons, and thus the seasonal year, are governed by the anomalistic year rather than the tropical year.
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