Difference between revisions of "Season"

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A season is a division of the year that has distinct weather, life patterns, and daylight. It is generally accepted that Earth has 4 seasons that vary in length and intensity depending on region. The seasonal change is caused by the Earth's orbit around the sun and the tilt of the Earth's axis (the "line" that it spins around). The seasons are opposite in the northern and southern hemispheres. So, when it is summer in Canada, for example, it is winter in Brazil. When it is summer in South Africa, it is winter in Germany. When it is winter in Australia, it is summer in Japan, and so on. This is because in May, June, and July, the northern hemisphere gets more sun and the southern hemisphere less due to the Earth's tilt making it summer in the north and winter in the south. The opposite is true in November, December, and January. Generally, there are 4 seasons - spring, summer, winter, and fall, although some cultures recognize 6 seasons (temperate regions) or 2 seasons (equatorial regions).

Causes[edit]

If you imagine the Earth orbiting the sun on a completely horizontal (flat) plane, you would notice that it does not exactly rotate vertically (straight up and down). That is, the horizontal orbiting and vertical rotation do not make a right (90 degree) angle. Instead, you would see that the Earth rotates on a tilt of 23.4 degrees away from the vertical line (axis). This axial tilt means that during part of the year, the polar ends of the earth get more sun. In fact, as you approach the poles, you would notice that in the height of summer, there is a stretch of time where there is 24 hours of sunlight! The opposite is also true in that in the dead of winter, there is a stretch of time with no sunlight at all. This causes 2 phenomena: the dramatic seasonal change of many regions and the opposite nature of the seasons between the northern and southern hemispheres. The less sunlight the region receives, the cooler it becomes. Plants that rely on sunlight to survive begin to die or go dormant. Animals that rely on plants also die or go dormant. Fall turns into winter and rains become snow. As the Earth makes its way around the sun, the region begins to get more exposure to the sun and warms up. Plants and animals come back to life as spring turns into summer.

Total Day/Night[edit]

The military and weather station Alert on the northern tip of Ellesmere Island, Canada, is less than 900 km from the North Pole and as such experiences extended periods of total day and total night. Specifically, on 6 April the sun rises at 5:20 am and remains above the horizon until it sets below the horizon again on 6 September. In effect, there are 5 months of complete daylight! Conversely, on October 14 the sun sets and does not rise again until 27 February.

Four Seasons[edit]

The most common way to divide the seasons is into 4. There are a few different ways of doing this.

Meteorological[edit]

Meteorological seasons are divided according to temperature, with summer being the hottest and winter being the coldest. The definition of seasons as 4 groupings of 3 months was established in 1780 and has been used ever since. According to this definition, spring begins on March first, summer on June first, fall on September first, and winter on December first in the northern hemisphere. In the southern hemisphere, spring begins on September first, summer on December first, autumn on March first, and winter on June first.

In Sweden and Finland, a different system is used. The definition is still based on temperature, but is not confined to the calendar months. For example, spring begins when the daily averaged temperature permanently rises above 0 °C, which means that the daily averaged temperature has remained above 0 for seven consecutive days. Summer is set at +10 °C, fall when the temperature falls below +10 °C, and winter is set at 0 °C. This means that the seasons do not begin at fixed dates but that they happen when they happen. Meteorologists (those who study the weather) must watch the weather and announce when the season has changed. This also means that it is possible for the seasons to change at different times in different parts of the country.

Astronomical[edit]

Astronomical seasons are also a common way to divide the seasons. This method uses the sun's passing over the the tropics of Cancer and Capricorn for the solstices (longest and shortest days of the year marking the beginning of summer and winter) and the sun's passing over the equator for the equinoxes (day and night of equal length or the beginning of spring and fall). According to this method, spring might begin at the point of equinox on the 19th, 20th, or 21st of March. Summer would begin at the point of solstice on the 20th or 21st of June. Fall would begin at the equinox on the 22nd or 23rd of September. Winder would begin at the solstice on the 21st or 22nd of December.

Solar[edit]

Similar to astronomical seasons, solar seasons are based on the equinoxes and solstices. However, instead of these points marking the beginning of the seasons, they mark their midpoints. For example, this is the system used in the traditional Chinese calendar. In this calendar, the seasons are: Lichun (立春, spring), beginning on about February 4th; Lixia (立夏, summer), beginning on about May 6th; Liqiu (立秋, fall), beginning on about August 8th; and Lidong (立冬, winter), beginning on about November 7th. The Celtic calendar also follows this system with the start of the seasons being associated with the four Pagan agricultural festivals. November first or Samhain, the Celtic origin of Halloween, begins winter. February first or Imbolc, the Celtic origin of Groundhog Day, begins spring. May first or Beltane, the Celtic origin of May Day, begins summer. August first or Lughnasadh begins fall.

Six Seasons[edit]

Some south Asian cultures use a 6-season calendar. In the Hindu calendar, for example, the seasons are Vasanta (spring), Greeshma (summer), Varsha (monsoon), Sharad (autumn), Hemanta (early winter), and Shishira (prevernal or late winter). Spring is mid-March to mid-May, summer is mid-May to mid-July, monsoon is mid-July to mid-September, fall is mid-September to mid-November, early winter is mid-November to mid-January, and late winter is mid-January to mid-March.

The Bengali and Tamil calendars are also 6-season calendars, but the dates are slightly different. Spring is mid-February to mid-April, summer is mid-April to mid-June, monsoon is mid-June to mid-August, fall is mid-August to mid-October, late fall is mid-October to mid-December, and winter is mid-December to mid-February.

Ecological Seasons[edit]

The seasons can also be divided based on what kind of animal and plant activities are happening. Hibernation, for example, happens in winter while flowers blooming happens in spring. Although the dates vary depending on which region one is in, the seasons are as follows:

  • Prevernal (early or pre-spring): Begins February (mild temperate), to March (cool temperate). Tree buds begin to appear. Some types of migrating birds fly from winter to summer homes.
  • Vernal (spring): Begins mid March (mild temperate), to late April (cool temperate). Tree buds burst into leaves. Birds mark territories and begin mating and nesting.
  • Estival (high summer): Begins June in most temperate climates. Trees are in full leaf. Birds hatch and raise babies.
  • Serotinal (late summer): Generally begins mid to late August. Leaves begin to change colour in northern locations. Birds get ready for autumn migration. The traditional "harvest season" begins by early September.
  • Autumnal (autumn): Generally begins mid to late September. Tree leaves are in full colour, then turn brown and fall to the ground. Birds migrate.
  • Hibernal (winter): Begins December (mild temperate), November (cool temperate). Trees are bare and fallen leaves begin to decay.

Indigenous people also tend to define seasons ecologically, with changing winds, flowering plants, or migration patterns marking the seasonal changes. In Australia, the Noongar people divide the seasons into first summer or the season of the young (December and January), second summer or the season of adolescence (February and March), fall or the season of adulthood (April and May), the first rains or fertility season (June and July), the second rains or season of conception (August and September) and wildflower season or the season of birth (October and November).

The Cree people of North America also use a 6-season system of winter (January and February), break-up (March and April), spring (May and June), summer (July and August), fall (September and October), and freeze-up (November and December).

Two Seasons[edit]

In tropical regions there might only be two seasons - wet and dry. The wet season in the northern hemisphere begins around April first and ends on September 30th with the beginning of the dry season. The dry season then lasts until March 31st. The opposite is true for the southern hemisphere.