Animals might prepare themselves for the upcoming cold weather, storing food or traveling to warmer regions. Various cultures have celebrated bountiful harvests with annual festivals. Thanksgiving is a good example. Winter often brings a chill. Some areas may experience snow or ice, while others see only cold rain.
- The annual cycle.
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Animals find ways to warm themselves, and may have changed their appearance to adapt. The Indian festival of Diwali, for example, which takes place between October and November, celebrates the triumph of righteousness, and of light over darkness. The timing and characteristics of the seasons depends upon the location on Earth.
Regions near the equator experience fairly constant temperatures throughout the year, with balmy winters barely discernible from warm summers. This is because it gets fairly constant light from the sun, due to its position on the outer curve of the Earth, according to the Atmospheric Radiation Measurement ARM program.
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For areas to the north and south, the seasons can change more significantly. People closer to the poles might experience icier, more frigid winters, while those closer to the equator might suffer hotter summers. Other factors can also affect the weather and temperature over the seasons; some areas experience dry summers as temperatures spike, while others might call summer their "wet season.
Mountainous regions might experience more snowfall than plains within the same latitude, while oceanfront property could see an increase in violent tropical storms as the weather shifts. The time of year a region experiences a season depends on whether it is in the northern or southern hemisphere. The Southern Hemisphere experiences winter while its northern neighbors chart summer; the north sees the slow blossom of spring while the south brings in the autumn harvest.
The cycle of seasons is caused by Earth's tilt toward the sun. The planet rotates around an invisible axis.
The Seasons (Haydn) - Wikipedia
At different times during the year, the northern or southern axis is closer to the sun. During these times, the hemisphere tipped toward the star experiences summer, while the hemisphere tilted away from the sun experiences winter, according to the National Oceanic and Atmospheric Administration NOAA. At other locations in Earth's annual journey, the axis is not tilted toward or away from the sun.
During these times of the year, the hemispheres experience spring and autumn.
The astronomical definition of the seasons relates to specific points in Earth's trip around the sun. The summer and winter solstice, the longest and shortest day of the year, occur when Earth's axis is either closest or farthest from the sun. The south's summer solstice occurs around December 21, the winter solstice for the north. In both hemispheres, the summer solstice marks the first day of astronomical summer, while the winter solstice is considered the first day of astronomical winter.
Equinoxes are another significant day during Earth's journey around the Sun. On these days, the planet's axis is pointed parallel to the Sun, rather than toward or away from it. Day and night during the equinoxes are supposed to be close to equal. The result is that the South Pole is consistently colder during the southern winter than the North Pole during the northern winter.
The seasonal cycle in the polar and temperate zones of one hemisphere is opposite to that of the other. When it is summer in the Northern Hemisphere, it is winter in the Southern, and vice versa.
The tropical and subtropical regions see little annual fluctuation of sunlight. As a result, the amount of precipitation tends to vary more dramatically than the average temperature. When the Zone is north of the Equator, the northern tropics experience their wet season while the southern tropics have their dry season.
This pattern reverses when the Zone migrates to a position south of the Equator. In meteorological terms, the solstices the maximum and minimum insolation do not fall in the middles of summer and winter. The heights of these seasons occur up to 7 weeks later because of seasonal lag. Seasons, though, are not always defined in meteorological terms. In astronomical reckoning by hours of daylight alone, the solstices and equinoxes are in the middle of the respective seasons.
Because of seasonal lag due to thermal absorption and release by the oceans, regions with a continental climate , which predominate in the Northern Hemisphere , often consider these four dates to be the start of the seasons as in the diagram, with the cross-quarter days considered seasonal midpoints.
The length of these seasons is not uniform because of Earth's elliptical orbit and its different speeds along that orbit. Calendar-based reckoning defines the seasons in absolute rather than relative terms. Accordingly, if floral activity is regularly observed during the coolest quarter of the year in a particular area, it is still considered winter despite the traditional association of flowers with spring and summer.
Additionally, the seasons are considered to change on the same dates everywhere that uses a particular calendar method regardless of variations in climate from one area to another. Most calendar-based methods use a four-season model to identify the warmest and coldest seasons, which are separated by two intermediate seasons. Meteorological seasons are reckoned by temperature, with summer being the hottest quarter of the year and winter the coldest quarter of the year. In the Societas Meteorologica Palatina which became defunct in , an early international organization for meteorology, defined seasons as groupings of three whole months as identified by the Gregorian calendar.
Ever since, professional meteorologists all over the world have used this definition.
For the southern hemisphere temperate zone, spring begins on 1 September, summer on 1 December, autumn on 1 March, and winter on 1 June. In Sweden and Finland, meteorologists use a non-calendar based definition for the seasons based on the temperature. This implies two things: This almost always occurred in March.
However, with global warming this temperature is now not uncommon in the winter. Astronomical timing as the basis for designating the temperate seasons dates back at least to the Julian calendar used by the ancient Romans. It continues to be used on many modern Gregorian calendars worldwide, although some countries like Australia, New Zealand, and Russia prefer to use meteorological reckoning. The precise timing of the seasons is determined by the exact times of transit of the sun over 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 following diagram shows the relation between the line of solstice and the line of apsides of Earth's elliptical orbit. The orbital ellipse with eccentricity exaggerated for effect goes through each of the six Earth images, which are sequentially the perihelion periapsis—nearest point to the sun on anywhere from 2 January to 5 January, the point of March equinox on 19, 20 or 21 March, the point of June solstice on 20 or 21 June, the aphelion apoapsis—farthest point from the sun on anywhere from 4 July to 7 July, the September equinox on 22 or 23 September, and the December solstice on 21 or 22 December.
These "astronomical" seasons are not of equal length, because of the elliptical nature of the orbit of the Earth, as discovered by Johannes Kepler. From the March equinox it currently takes 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. They are reset by the occurrence of a leap year. The Gregorian calendar is designed to keep the March equinox no later than 21 March as accurately as is practical.
Gregorian calendar seasonal error. The calendar equinox used in the calculation of Easter is 21 March, the same date as in the Easter tables current at the time of the Council of Nicaea in AD The calendar is therefore framed to prevent the astronomical equinox wandering onto 22 March. From Nicaea to the date of the reform, the years , , , , , , , and , which would not have been leap years in the Gregorian calendar, amount to nine days, but astronomers directed that ten days be removed.
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 the century progresses. This shift is a full day in about years compensated mainly by the century "leap year" rules of the Gregorian calendar and as was a leap year the current shift has been progressing since the beginning of the last century, when equinoxes and solstices were relatively late.
Location, location, location
This also means that in many years of the twentieth century, the dates of 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. On the other hand, people living far to the west America whose clocks run behind UTC may experience an equinox as early as March Over thousands of years, the Earth's axial tilt and orbital eccentricity vary see Milankovitch cycles. The equinoxes and solstices move westward relative to the stars while the perihelion and aphelion move eastward. Thus, ten thousand years from now Earth's northern winter will occur at aphelion and northern summer at perihelion.
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 Smaller irregularities in the times are caused by perturbations of the Moon and the other planets. Solar timing is based on insolation in which the solstices and equinoxes are seen as the midpoints of the seasons. It was the method for reckoning seasons in medieval Europe, especially by the Celts , and is still ceremonially observed in Ireland and some east Asian countries.
Summer is defined as the quarter of the year with the greatest insolation and winter as the quarter with the least. 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. Thus, the day of greatest insolation is designated "midsummer" as noted in William Shakespeare 's play A Midsummer Night's Dream , which is set on the summer solstice.
On the Celtic calendar , the start of the seasons corresponds to four Pagan agricultural festivals - the traditional first day of winter is 1 November Samhain , the Celtic origin of Halloween ; spring starts 1 February Imbolc , the Celtic origin of Groundhog Day ; summer begins 1 May Beltane , the Celtic origin of May Day ; the first day of autumn is 1 August Celtic Lughnasadh.
The traditional calendar in China forms the basis of other such systems in East Asia.
Its seasons are traditionally based on 24 periods known as solar terms. These dates were not part of the traditional lunar calendar, however, and moveable holidays such as Chinese New Year and the Mid-Autumn Festival are more closely associated with the seasons. Some calendars in south Asia use a six-season method where the number of seasons between summer and winter can number from one to three.
The dates are fixed at even intervals of months. In the Hindu calendar of tropical and subtropical India, there are six seasons or Ritu that are calendar-based in the sense of having fixed dates: Vasanta spring , Greeshma summer , Varsha monsoon , Sharad autumn , Hemanta early winter , and Shishira prevernal or late winter. The six seasons are ascribed to two months each of the twelve months in the Hindu calendar. The rough correspondences are:. The Bengali Calendar is similar but differs in start and end times.
It has the following seasons or ritu:. The Tamil calendar follows a similar pattern of six seasons. The Noongar people of South-West Western Australia also recognise maar-keyen bonar  , or six seasons. 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 seasons also correlate to aspects of the human condition, intrinsically linking the lives of the people to the world that surrounds them and also dictating their movements, as with each season, various parts of country would be visited which were particularly abundant or safe from the elements. The timing and feel of the seasons has been noted as having changed due to the current trends in climate change. The North American Cree and possibly other Algonquian speaking peoples used or still use a 6 season system. The extra two seasons denoting the freezing and breaking up of the ice on rivers and lakes.
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.
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At progressively higher latitudes, the maximum periods of " midnight sun " and " polar night " are progressively longer. 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. 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.
From mid-November to mid-January, there is no twilight. In the weeks surrounding 21 June, in the northern polar region, the sun is at its highest elevation, appearing to circle the sky there without going below the horizon. 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.
For a few more weeks, "day" is marked by decreasing periods of twilight. Eventually, from mid-November to mid-January, there is no twilight and it is continuously dark.
In mid January the first faint wash of twilight briefly touches the horizon for just minutes per day , and then twilight increases in duration with increasing brightness each day until sunrise at end of February, then on 6 April the sun remains above the horizon until mid October. Ecologically speaking, a season is a period of the year in which only certain types of floral and animal events happen e.
In this sense, ecological seasons are defined in absolute terms, unlike calendar-based methods in which the seasons are relative. If specific conditions associated with a particular ecological season don't normally occur in a particular region, then that area cannot be said to experience that season on a regular basis. Six seasons can be distinguished which do not have fixed calendar-based dates like the meteorological and astronomical seasons.