Season 28919 225655742 2008-07-14T19:30:18Z SoWhy 54890 Reverted edits by [[Special:Contributions/86.7.170.1|86.7.170.1]] to last version by SieBot (using [[WP:HG|Huggle]]) {{Otheruses}} {{Weather nav}} A '''season''' is one of the major divisions of the [[year]], generally based on yearly periodic changes in [[weather]]. Seasons happen due to the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution. In Temperate and Polar regions, the seasons are marked by changes in the amount of sunlight which may cause animals to go into hibernation or to migrate, and plants to be dormant. The Northern hemisphere is closer to the sun at times of the year than the southern, it is exposed to more light causing summer to come into action at different times as the earth revolves. In [[temperate]] and [[Polar climate|polar]] regions generally four seasons are recognized: ''[[Spring (season)|spring]]'', ''[[summer]]'', ''[[autumn]]'', ''[[winter]]''. In some [[tropics|tropical]] and [[subtropical]] regions it is more common to speak of the [[wet season|rainy]] (or wet, or [[monsoon]]) season versus the [[dry season]], because the amount of [[Precipitation (meteorology)|precipitation]] may vary more dramatically than the average temperature. In other tropical areas a three-way division into hot, rainy and cool season is used. In some parts of the world, special "seasons" are loosely defined based upon important events such as a [[hurricane]] season, [[tornado]] season or a [[wildfire]] season. <!--[[Image:north season.jpg|thumb|400px|Diagram of the Earth's seasons as seen from the north. Far right: December solstice]] [[Image:south season.jpg|thumb|400px|Diagram of the Earth's seasons as seen from the south. Far left: June solstice]]--> <!--[[Image:seasons3.svg|frame|right|'''Fig. 2'''<br/>As the Earth revolves around the Sun, the seasons in the northern and southern hemispheres are opposite.]]--> ==Causes and effects== [[Image:Seasonearth.png|thumb|right|275px|Illumination of the earth during various seasons]] [[Image:seasons.svg|frame|right|'''Fig. 1'''<br/>This is a diagram of the seasons, regardless of the time of day (i.e. the [[Earth]]'s rotation on its axis), the [[North Pole]] will be dark, and the [[South Pole]] will be illuminated; see also [[arctic winter]]. In addition to the density of [[Angle of incidence|incident]] light, the [[dissipation]] of light in the [[Earth's atmosphere|atmosphere]] is greater when it falls at a shallow angle.]] {{Main|Effect of sun angle on climate}} The seasons result from the [[Earth]]'s [[axis of rotation|axis]] being [[axial tilt|tilted]] to its [[orbital plane (astronomy)|orbital plane]]; it deviates by an angle of approximately 23.5 [[degree (angle)|degree]]s. Thus, at any given time during summer or winter, one part of the planet is more directly exposed to the rays of the [[Sun]] (see ''Fig. 1''). This exposure alternates as the Earth revolves in its orbit. At any given time, regardless of season, the [[northern hemisphere|northern]] and [[southern hemisphere]]s experience opposite seasons. It is easy to observe the effect of the axis tilt from the change in [[day length]], and [[altitude (astronomy)|altitude]] of the Sun at [[noon]] (the [[culmination]] of the Sun), during a [[year]]. Seasonal weather differences between hemispheres are further caused by the [[Kepler's laws of planetary motion|elliptical orbit]] of Earth. Earth reaches [[perihelion]] (the point in its orbit closest to the [[Sun]]) in January, and it reaches [[aphelion]] (farthest point from the Sun) in July. Even though the effect this has on Earth's seasons is minor, it does noticeably soften the northern hemisphere's winters and summers. In the southern hemisphere, the opposite effect is observed. Seasonal weather fluctuations (changes) also depend on factors such as proximity to [[ocean]]s or other large bodies of water, [[ocean current|current]]s in those oceans, [[El Niño-Southern Oscillation|El Niño]]/ENSO and other oceanic cycles, and prevailing [[wind]]s. In the temperate and polar regions, seasons are marked by changes in the amount of [[sunlight]], which in turn often causes [[Biological life cycle|cycles]] of dormancy in plants and [[hibernation]] in animals. These effects vary with latitude and with proximity to bodies of water. 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 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. In the [[tropic]]s, there is no noticeable change in the amount of sunlight. However, many regions (such as the northern [[Indian ocean]]) are subject to [[monsoon]] [[rain]] and wind cycles. A study of temperature records over the past 300 years<ref>David Thomson, ''[[Science (journal)|Science]]'', April 1995</ref> shows that the climatic seasons, and thus the [[seasonal year]], are governed by the [[Year#Astronomical years|anomalistic year]] rather than the [[tropical year]]. In meteorological terms, the summer [[solstice]] and winter solstice (or the maximum and minimum [[insolation]], respectively) do not fall in the middles of summer and winter. The heights of these seasons occur up to a month later because of [[seasonal lag]]. Seasons, though, are not always defined in meteorological terms. Compared to axial tilt, other factors contribute little to seasonal temperature changes. The seasons are not the result of the variation in [[Earth]]’s distance to the sun because of its [[elliptical orbit]].<ref>"Fundamentals of physical geography", ''PhysicalGeography.net'', Ch. 6: Energy and Matter:(h) Earth-Sun Geometry, [http://www.physicalgeography.net/fundamentals/6h.html]</ref> [[Orbital eccentricity]] can influence temperatures, but on Earth, this effect is small and is more than counteracted by other factors; research shows that the Earth as a whole is actually slightly warmer when ''farther'' from the sun.<ref>Phillips, Tony, "[http://science.nasa.gov/headlines/y2002/02jul_aphelion.htm The Distant Sun (Strange but True: the Sun is far away on the 4th of July)]," [http://science.nasa.gov/default.htm Science@NASA], downloaded 24 June 2006</ref> [[Mars#Climate|Mars]] however experiences wide temperature variations and [http://descanso.jpl.nasa.gov/Propagation/mars/MarsPub020318.pdf violent dust storms] every year at perihelion.<ref name="HoGolshanKliore_02_5_59_60">Christian Ho, Nasser Golshan, and Arvydas Kliore, ''[http://descanso.jpl.nasa.gov/Propagation/mars/MarsPub_sec1.pdf Radio Wave Propagation Handbook for Communication on and Around Mars]'', JPL Publication 02-5, pp. 59-60, downloaded 23 June 2006.</ref> ==Polar day and night== Any point north of the [[Arctic Circle]] or south of the [[Antarctic Circle]] will have one period in the summer when the sun does not set, and one period in the winter when the sun does not rise. At progressively higher latitudes, the periods of "[[midnight sun]]" (or "midday dark" for the other side of the globe) are progressively longer. For example, at the military and weather station [[Alert, Nunavut|Alert]] on the northern tip of [[Ellesmere Island]], [[Canada]] (about 450 [[nautical mile]]s or 830 [[kilometre|km]] from the [[North Pole]]), the sun begins to peek above the horizon in mid-February and each day it climbs higher and stays up longer; by [[21 March]], the sun is up for 12 hours. However, mid-February is not first light. The sky (as seen from Alert) has [[twilight]], or at least a pre-dawn glow on the horizon, for increasing hours each day, for more than a month before the sun first appears. In the weeks surrounding [[21 June]], the sun is at its highest, and it appears to circle the sky without going below the horizon. Eventually, it does go below the horizon, for progressively longer periods each day until, around the middle of October, it disappears for the last time. For a few more weeks, "day" is marked by decreasing periods of twilight. Eventually, for the weeks surrounding [[21 December]], it is continuously dark. In later winter, the first faint wash of light briefly touches the horizon (for just minutes per day), and then increases in duration and pre-dawn brightness each day until sunrise in February. ==3D Simulation== It is possible to explore interactively in [http://www.boutichesaid.cv.dz/Earth/EarthLight/EarthLight.htm this 3D season simulation], the main elements of this article such as: *Effect of sun angle on climate, *tilt of the earth's axe of poles, *Polar day and night *Earth in 3D light ==Reckoning== ===Meteorological=== Meteorological seasons are reckoned by temperature, with summer being the hottest quarter of the year and winter the coldest quarter of the year. Using this reckoning, the [[Roman calendar]] began the year and the spring season on the first of March, with each season occupying three months. This reckoning is also used in [[Denmark]], the former [[USSR]], and [[Australia]]. In the modern [[United Kingdom]] there are no hard and fast rules about seasons, and informally many people use this reckoning. So, in meteorology for the Northern hemisphere: spring begins on [[March 1]], summer on [[June 1]], autumn on [[September 1]], and winter on [[December 1]]. Conversely, for the Southern hemisphere: summer begins on [[December 1]], autumn on [[March 1]], winter on [[June 1]], and spring on [[September 1]]. ===Astronomical=== [[Image:Seasons1.svg|center|600px]] In [[Astronomy|astronomical]] reckoning, the seasons begin at the [[solstice]]s and [[equinox]]es. The [[cross-quarter day]]s are considered seasonal midpoints. The length of these seasons is not uniform because of the elliptical orbit of the earth and its [[Kepler's laws of planetary motion|different speeds along that orbit]].{{Fact|date=April 2008}} In the conventional United States calendar: Winter (89 days) begins on [[21 December]], the winter solstice; spring (92 days) on [[20 March]], the vernal equinox; summer (93 days) on [[20 June]], the summer solstice; and autumn (90 days) on [[22 September]], the autumnal equinox.{{Fact|date=April 2008}} Because of the differences in the Northern and Southern Hemispheres, it is no longer considered appropriate to use the northern-seasonal designations for the astronomical quarter days. The modern convention for them is: March Equinox; June Solstice; September Equinox; and December Solstice ===Traditional=== Traditional seasons are reckoned by [[insolation]], with summer being the quarter of the year with the greatest insolation and winter the quarter with the least. These seasons begin about 4 weeks earlier than the meteorological seasons and 7 weeks earlier than the astronomical seasons. In traditional reckoning, the seasons begin at the [[cross-quarter day]]s. The solstices and equinoxes are the ''midpoints'' of these seasons. For example, the days of greatest and least insolation are considered the "midsummer" and "midwinter" respectively. This reckoning is used by various traditional cultures in the Northern Hemisphere, including [[solar term|East Asian]] and Irish cultures. In [[Iran]], [[Afghanistan]] and some other parts of middle east the beginning of the astronomical spring is the beginning of the new year which is called [[Nowruz]]. So, according to traditional reckoning, winter begins between [[5 November]] and [[10 November]], [[Samhain]], [[立冬]] (lìdōng or rittou); spring between [[2 February]] and [[7 February]], [[Imbolc]], [[立春]] (lìchūn or rissyun); summer between [[4 May]] and [[10 May]], [[Beltane]], [[立夏]] (lìxià or rikka); and autumn between [[3 August]] and [[10 August]], [[Lughnasadh]], [[立秋]] (lìqiū or rissyuu). The middle of each season is considered Mid-winter, between [[20 December]] and [[23 December]], [[冬至]] (dōngzhì or touji); Mid-spring, between [[19 March]] and [[22 March]], [[春分]] (chūnfēn or syunbun); Mid-summer, between [[19 June]] and [[23 June]], [[夏至]] (xiàzhì or geshi); and Mid-autumn, between [[21 September]] and [[24 September]], [[秋分]] (qiūfēn or syuubun). . ===Australia=== In [[Australia]], the traditional aboriginal people defined the seasons by what was happening to the plants, animals and weather around them. This led to each separate tribal group having different seasons, some with up to 8 seasons each year. However, most modern [[Aborigine|Aboriginal Australians]] follow the meteorological seasons as do non-Aboriginal Australians. == In art== The (four) seasons have inspired many artists. Below is a list of some notable artwork about this theme: *[[The Four Seasons (Vivaldi)]] *[[The Seasons (poem)]] *[[Spring, Summer, Autumn, Winter... and Spring|Spring, Summer, Autumn, Winter… and Spring]] == See also == *[[Perennial tea ceremony]] *[[Months]] ==References== {{reflist}} ==External links== *[http://www.cultureandrecreation.gov.au/articles/weather/ Australian Weather and Seasons] *[http://www.badastronomy.com/bad/misc/badseasons.html When do the Seasons Begin?] (from the [[Bad Astronomer]]) *[http://www.straightdope.com/classics/a1_170b.html Solstice does not signal season's start] (from [[The Straight Dope]]) *[http://www.bbc.co.uk/dna/h2g2/A526673 Why the Earth has seasons] article on [[h2g2]]. *[http://www.deh.gov.au/parks/kakadu/artculture/seasons.html Aboriginal seasons of Kakadu] *[http://www.bom.gov.au/iwk/climate_culture/Indig_seasons.shtml Indigenous seasons (Australian Bureau of Meteorology)] *[http://www.stirling.au.com/educ/traditional_culture.pdf Mt Stirling Seasons] *[http://www.abc.net.au/science/features/indigenous/ The Lost Seasons] *[http://home.vicnet.net.au/~herring/seasons.htm Melbourne's six seasons] *[http://www.sym454.org/seasons/ The Lengths of the Seasons] (numerical integration analysis) *[http://www.badastronomy.com/bad/misc/seasons.html] (Earth distance vs tilt) {{Seasons}} {{Koppen}} [[Category:Calendars]] [[Category:Climatology]] [[Category:Climate]] [[Category:Seasons| ]] [[Category:Units of time]] [[ar:فصول السنة]] [[ast:Estación del añu]] [[gn:Arajere]] [[bs:Godišnje doba]] [[ca:Estació de l'any]] [[cv:Çанталăк тапхăрĕсем]] [[cs:Roční období]] [[da:Årstid]] [[de:Jahreszeit]] [[et:Aastaajad]] [[el:Εποχές]] [[es:Estación del año]] [[eo:Sezono]] [[eu:Urtaro]] [[fr:Saison]] [[gl:Estación do ano]] [[zh-classical:四季]] [[ko:계절]] [[hi:ऋतु]] [[hr:Godišnja doba]] [[id:Musim]] [[ia:Station del anno]] [[is:Árstíð]] [[it:Stagione]] [[he:עונות השנה]] [[ht:Sezon]] [[la:Tempora anni]] [[lv:Gadalaiks]] [[lt:Metų laikai]] [[ln:Eleko]] [[hu:Évszak]] [[mr:ऋतू]] [[nl:Seizoen]] [[cr:Kâ-isiwepahki]] [[ja:季節]] [[no:Årstid]] [[nn:Årstid]] [[nrm:Saîson]] [[pl:Pora roku]] [[pt:Estação do ano]] [[qu:Mit'a]] [[ru:Времена года]] [[simple:Season]] [[sl:Letni časi]] [[so:Afarta xilli]] [[sh:Godišnje doba]] [[fi:Vuodenaika]] [[sv:Säsong]] [[th:ฤดู]] [[vi:Mùa]] [[tr:Mevsim]] [[uk:Пора року]] [[wa:Såjhon]] [[bat-smg:Metu laikā]] [[zh:季节]]