The beginning of spring is defined as when the mean daily temperature permanently rises above 0 °C. In Sweden and Finland, meteorologists and news outlets use the concept of thermal seasons, which are defined based on mean daily temperatures. These are mainly a matter of custom and not generally proclaimed by governments north or south of the equator for civil purposes.
This also means that in many years of the twentieth century, the dates March 21, June 22, September 23, and December 22 were much more common, so older books teach (and older people may still remember) these dates. The times of the equinoxes and solstices are not fixed with respect to the modern Gregorian calendar, but fall about six hours later every year, amounting to one full day in four years. Thus the time from the March equinox to the September equinox is 7.56 days longer than from the September equinox to the March equinox.

Meteorological

From the March equinox it currently takes 92.75 days until the June solstice, then 93.65 days until the September equinox, 89.85 days until the December solstice and finally 88.99 days until the March equinox. He gives “the eighth day to the Kalends of January” (December 25) as the date of the winter solstice, though actually it occurred on the 22nd or 23rd at that time. He then defines the seasons of autumn, winter, spring, and summer as starting half-way through these intervals. He points out that the lengths are not equal, being 91 (in non-leap years), 94, 91, and 89 days for spring, summer, autumn, and winter, respectively. This means that areas with relatively extreme climates (such as the Paracel Islands and parts of the Tibetan Plateau) may be said to have summer all year round or winter all year round. The beginning of summer is defined as when the temperature permanently rises above +10 °C, autumn as when the temperature permanently falls below +10 °C, and winter as when the temperature permanently falls below 0 °C.

Change over time

It is Earth’s axial tilt that causes the Sun to be higher in the sky during the summer months, which increases the solar flux. The Northern Hemisphere experiences most direct sunlight during May, June, and July (thus the traditional celebration of Midsummer in June), as the hemisphere faces the Sun. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth’s surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant.

  • 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.
  • Eventually, it does go below the horizon, for progressively longer periods each day until around the middle of October, when it disappears for the last time until the following February.
  • The precise timing of the seasons is determined by the exact times of the Sun reaching the tropics of Cancer and Capricorn for the solstices and the times of the Sun’s transit over the equator for the equinoxes, or a traditional date close to these times.
  • The Noongar people of South-West Western Australia recognise maar-keyen bonar, or six seasons.
  • Calendar-based reckoning defines the seasons in relative rather than absolute terms, so the coldest quarter-year is considered winter even if floral activity is regularly observed during it, despite the traditional association of flowers with spring and summer.
  • In Australia, some tribes have up to eight seasons in a year, as do the Sami people in Scandinavia.

Four-season reckoning

A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. COVID-19 is on the upswing in California and across a swath of the West and the South, a sign that the virus may be starting its seasonal summer uptick. Start your learning journey today with our library of interactive, themed word lists built by the experts at Vocabulary.com – we’ll help you make the most of your study time!
Indigenous people in polar, temperate and tropical climates of northern Eurasia, the Americas, Africa, Oceania, and Australia have traditionally defined the seasons ecologically by observing the activity of the plants, animals and weather around them. The precise timing of the seasons is determined by the exact times of the Sun reaching the tropics of Cancer and Capricorn for the solstices and the times of the Sun’s transit over the equator for the equinoxes, or a traditional date close to these times. The four seasons have been in use since at least Roman times, as in Rerum rusticarum of Varro Varro says that spring, summer, autumn, and winter start on the 23rd day of the sun’s passage through Aquarius, Taurus, Leo, and Scorpio, respectively. Floral and animal activity variation near the equator depends more on wet/dry cycles than seasonal temperature variations, with different species flowering (or emerging from cocoons) at specific times before, during, or after the monsoon season. There is no noticeable change in the amount of sunlight at different times of the year.
The North American Cree and possibly other Algonquian speaking peoples used or still use a 6-season system. In Australia, some tribes have up to eight seasons in a year, as do the Sami people in Scandinavia. Oceanic regions tend to experience the beginning of the hibernal season up to a month later than continental climates. Six ecological seasons can be distinguished without fixed calendar-based dates like the meteorological and astronomical seasons. In this sense, ecological seasons are defined in absolute terms, unlike calendar-based methods in which the seasons are relative.
In general, the effect of orbital eccentricity on Earth’s seasons is a 7% variation in sunlight received. Between this effect and the shorter daylight hours, the axial tilt of the Earth accounts for most of the seasonal variation in climate in both hemispheres. The effect of axial tilt is observable as the change in day length and the altitude of the Sun at solar noon (the Sun’s culmination) during the year. Regardless of the time of year, the Northern Hemisphere and Southern Hemisphere always experience opposite seasons. Because of seasonal lag, June, July, and August are the warmest months in the Northern Hemisphere while December, January, and February are the warmest months in the Southern Hemisphere.

Meteorological

  • Between this effect and the shorter daylight hours, the axial tilt of the Earth accounts for most of the seasonal variation in climate in both hemispheres.
  • The severity of seasonal change — the average temperature difference between summer and winter in location — will also change over time because the Earth’s axial tilt fluctuates between 22.1 and 24.5 degrees.
  • The solar seasons change at the cross-quarter days, which are about 3–4 weeks earlier than the meteorological seasons and 6–7 weeks earlier than seasons starting at equinoxes and solstices.
  • In the tropical parts of Australia in the northern parts of Queensland, Western Australia, and the Northern Territory, wet and dry seasons are observed in addition to or in place of temperate season names.
  • Summer is defined as the quarter of the year with the greatest insolation and winter as the quarter with the least.
  • The traditional calendar in China has 4 seasons based on 24 periods, twelve of which are called zhōngqi and twelve of which are known as jiéqi.
  • According to this definition, for temperate areas in the northern hemisphere, spring begins on 1 March, summer on 1 June, autumn on 1 September, and winter on 1 December.

At the present time, the astronomical timing has winter starting at the winter solstice, spring at the spring equinox, and so on. As mentioned above, Varro wrote that spring, summer, autumn, and winter start on the 23rd day of the Sun’s passage through Aquarius, Taurus, Leo, and Scorpio, respectively, and that (in the Julian Calendar) these days were February 7, May 9, August 11, and November 10. Astronomical timing as the basis for designating the temperate seasons dates back at least to the Julian Calendar used by the ancient Romans.
Calendar-based reckoning defines the seasons in relative rather than absolute terms, so the coldest quarter-year is considered winter even if floral activity is regularly observed during it, despite the traditional association of flowers with spring and summer. As a result, the amount of precipitation tends to vary more dramatically than the average temperature or daylight hours. The slight differences between the solstices and the equinoxes cause seasonal shifts along a rainy low-pressure belt called the Intertropical Convergence Zone (ICZ). The seasonal cycle in the polar and temperate zones of one hemisphere is opposite to that of the other. Seasonal weather fluctuations (changes) 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.

First light comes in late January because the sky has twilight, being a glow on the horizon, for increasing hours each day, for more than a month before the Sun first appears with its disc above the horizon. By October 13 the Sun is above the horizon for only 1 hour 30 minutes, and on October 14 it does not rise above the horizon at all and remains below the horizon until it rises again on 27 February. On 6 April the Sun is perceived as rising at 0522 UTC and remains above the horizon until it sets below the horizon again on 6 September at 0335 UTC. At progressively higher latitudes, the maximum periods of “midnight sun” and “polar night” are progressively longer.
For example, in Nicaragua the dry season (November to April) is called “summer” and the rainy season (May to October) is called “winter”, even though it is located in the northern hemisphere. Each season’s arrival is heralded not by a calendar date, but by environmental factors such as changing winds, flowering plants, temperature and migration patterns and lasts approximately two standard calendar months. The Noongar people of South-West Western Australia recognise maar-keyen bonar, or six seasons.

The six seasons are ascribed https://royaldogs-ca.com/ to two months each of the twelve months in the Hindu calendar. In Europe, this is related to the English concept of Midsummer, High Summer or the Dog days, and related also to Spanish distinctions between primavera, estío and verano. Astronomically, the seasons are said to begin on Lichun (立春, “the start of spring”) on about 4 February, Lixia (立夏) on about 6 May, Liqiu (立秋) on about 8 August, and Lidong (立冬) on about 8 November. The traditional calendar in China has 4 seasons based on 24 periods, twelve of which are called zhōngqi and twelve of which are known as jiéqi. Summer is defined as the quarter of the year with the greatest insolation and winter as the quarter with the least. The severity of seasonal change — the average temperature difference between summer and winter in location — will also change over time because the Earth’s axial tilt fluctuates between 22.1 and 24.5 degrees.
People living farther to the east (Asia and Australia), whose local times are in advance, see the astronomical seasons apparently start later; for example, in Tonga (UTC+13), an equinox occurred on September 24, 1999, a date on which the equinox will not fall again until 2103. Currently, the most common equinox and solstice dates are March 20, June 21, September 22 or 23, and December 21; the four-year average slowly shifts to earlier times as a century progresses. As noted, a variety of dates and even exact times are used in different countries or regions to mark changes of the calendar seasons. Pre-modern armies, especially in Europe, tended to campaign in the summer months – peasant conscripts tended to melt away at harvest time, nor did it make economic sense in an agricultural society to neglect the sowing season. Seasonal weather and climate conditions can become important in the context of military operations.