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Spring •
Summer • •
Autumn •
Winter • •
Dry season • •
Wet season •
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Thunderstorm •
Tornado •
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Tropical Cyclone (Hurricane) •
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Winter storm •
Blizzard •
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Fog •
Drizzle •
Rain • •
Freezing rain •
Sleet • •
Hail •
Snow •
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Meteorology • •
Weather forecasting • •
Climate •
Air pollution •
A
season is one of the major divisions of the
year, generally based on yearly periodic changes in weather.
In
temperate and
polar regions generally four seasons are recognized:
spring,
summer,
autumn (
fall), and
winter.
In some
tropical and
subtropical regions it is more common to speak of the
rainy (or wet, or
monsoon) season versus the
dry season, as the amount of
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.
The seasons result from the
Earth's
axis being
tilted to its
orbital plane; it deviates by an angle of approximately 23.44
degrees. 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 and
southern hemispheres experience opposite seasons (see
Fig. 2 and
Month ranges of seasons (below) and
Effect of sun angle on climate).
Seasonal weather fluctuations also depend on factors such as proximity to
oceans or other large bodies of
water,
currents in those oceans,
El Niño/ENSO and other oceanic cycles, and prevailing
winds.
In the temperate and polar regions, seasons are marked by changes in the amount of
sunlight, which in turn often causes
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 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.
In the
tropics, there is no noticeable change in the amount of sunlight. However, many regions (famously the northern
Indian Ocean) are subject to
monsoon rain and wind cycles. Curiously, a study of temperature records over the past 300 years (David Thomson,
Science, April 1995) shows that the climatic seasons, and thus the
seasonal year, are governed by the
anomalistic year rather than the
tropical year.
In
meteorological terms, the winter
solstice and summer solstice (or the date maximum/minimum
insolation) do not fall in the middle of winter and summer respectively. The heights of these seasons occur up to a month later due to
seasonal lag. Seasons though, are not always defined in meteorological terms;
see reckoning Compared to axial tilt, other factors contribute little to seasonal temperature changes. It's a common misconception that the seasons are the result of the variation in
Earth's distance to the sun due to its
elliptical orbit.
In astronomical reckoning, the seasons begin at the
solstices and
equinoxes. The
cross-quarter days are considered seasonal midpoints. The length of these seasons is not uniform because of the elliptical orbit of the earth and its different speeds along that orbit (see
Kepler's laws).
In the conventional United States calendar:
Because of the differences in the Northern and Southern Hemispheres (see Meteorological below), it is no longer considered appropriate to use the old northern-seasonal designations for the astronomical quarter days. The modern convention for them is:
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 Ancient
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 modern
United Kingdom and
Ireland there are no hard and fast rules about seasons, and informally many people use this reckoning.
So, in
meteorology for the Northern hemisphere:
Conversely, for the Southern hemisphere:
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 days. 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
East Asian and Irish cultures.
So, according to Traditional reckoning,
And, the middle of each season is considered,
In
Australia, the aboriginal people defined the seasons by what was happening to the plants, animals and weather around them. This led to each separate tribal group have different seasons, some with up to 8 seasons a year. However, most modern Aboriginal Australians follow the Meteorological Seasons, as is conventional amongst non-Aboriginal Australians.
In
hemiboreal and
temperate climates:
In winter, the plant can't hold the leaves without Chloryphyll.
In spring, the plants produce Chloryphyll and start to grow again.
In summer, the plants grow. Usually at this time the plants completely mature.
In autumn, the trees stop making Chloryphyll and turn yellow or shades of orange and red then drop their leaves.
Temperate:
Spring · Summer · Autumn/Fall · Winter Tropical:
Dry season · Wet season Winter (89 days) begins on 21-22 Dec, the winter solstice
Spring (92 days) on 20-21 Mar, the spring equinox
Summer (93 days) on 20-21 June, the summer solstice
Autumn (90 days) on 22-23 Sept, the autumn equinox
The March Equinox
The June Solstice
The September Equinox
The December Solstice
spring begins on
March 1,
summer on
June 1,
autumn on
September 1, and
winter on
December 1.
summer begins on
December 1,
autumn on
March 1,
winter on
June 1, and
spring on
September 1.
Winter begins on 5-10 Nov,
Samhain,
立冬 (lìdōng),
Spring on 2-7 Feb,
Imbolc,
立春 (lìchūn),
Summer on 4-10 May,
Beltane,
立夏 (lìxià), and
Autumn on 3-10 Aug,
Lughnasadh,
立秋 (lìqiū).
Mid-winter: 20-23 Dec,
winter solstice,
冬至 (dōngzhì)
Mid-spring: 19-22 Mar,
spring equinox,
春分 (chūnfēn)
Mid-summer: 19-23 June,
summer solstice,
夏至 (xiàzhì)
Mid-autumn: 21-24 Sept,
autumn equinox,
秋分 (qiūfēn)
Perennial tea ceremony Sports season Australian Weather and Seasons When do the Seasons Begin? (from the
Bad Astronomer)
Solstice does not signal season's start (from
The Straight Dope)
Why the Earth has seasons article on
h2g2.
Aboriginal seasons of Kakadu Indigenous seasons (Australian Bureau of Meteorology) Mt Stirling Seasons The Lost Seasons Melbourne's six seasons The Lengths of the Seasons (numerical integration analysis)
Current members
Prominent writings
The era of Russian palace revolutions
Nimitz in popular culture