Season

seasonsseasonalfour seasonsseasonallyseasonal cycleThe Four Seasonsaseasonal2020-21agricultural yearall-season
A season is a division of the year marked by changes in weather, ecology, and the amount of daylight.wikipedia
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Earth

Earth's surfaceterrestrialworld
On Earth, seasons are the result of Earth's orbit around the Sun and Earth's axial tilt relative to the ecliptic plane.
Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth.

Axial tilt

obliquityobliquity of the eclipticaxis
On Earth, seasons are the result of Earth's orbit around the Sun and Earth's axial tilt relative to the ecliptic plane. Over thousands of years, the Earth's axial tilt and orbital eccentricity vary (see Milankovitch cycles).
This causes one pole to be directed more toward the Sun on one side of the orbit, and the other pole on the other side—the cause of the seasons on Earth.

Summer

summer seasonaustral summersummers
In temperate and sub-polar regions, four seasons based on the Gregorian calendar are generally recognized: spring, summer, autumn or fall, and winter.
Summer is the hottest of the four temperate seasons, falling after spring and before autumn.

Winter

austral wintermeteorological winterwintering
In temperate and sub-polar regions, four seasons based on the Gregorian calendar are generally recognized: spring, summer, autumn or fall, and winter.
Winter is the coldest season of the year in polar and temperate zones (winter does not occur in most of the tropical zone).

Ritu (Indian season)

RituWarshāRutu
In India from the ancient times, six seasons or Ritu based on south Asian religious or cultural calendars are recognised and identified even today for the purposes such as agriculture and trade. 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).
Ritu defines "season" in different ancient Indian calendars used in countries of India, Bangladesh, Nepal and Sri Lanka, and there are six ritus (also transliterated rutu) or seasons.

Autumn

fallautumn seasonAki
In temperate and sub-polar regions, four seasons based on the Gregorian calendar are generally recognized: spring, summer, autumn or fall, and winter.
Autumn, also known as fall in North American English, is one of the four temperate seasons.

Temperate climate

temperatetemperate zonetemperate zones
In temperate and sub-polar regions, four seasons based on the Gregorian calendar are generally recognized: spring, summer, autumn or fall, and winter.
These zones generally have wider temperature ranges throughout the year and more distinct seasonal changes compared to tropical climates, where such variations are often small.

Harmattan

Harmattan Windsharmattans
Some have a third cool, mild, or harmattan season.
The Harmattan is a season in the West African subcontinent, which occurs between the end of November and the middle of March.

Migration (ecology)

migrationmigratorymigrate
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.
Migration is often cyclical, frequently occurring on a seasonal basis, and in some cases on a daily basis.

Year

myaMay
The effect of axial tilt is observable as the change in day length and altitude of the Sun at solar noon (the Sun's culmination) during the year.
Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hours of daylight, and, consequently, vegetation and soil fertility.

Earth's orbit

orbitEarth orbitsEarth-Sun distance
On Earth, seasons are the result of Earth's orbit around the Sun and Earth's axial tilt relative to the ecliptic plane.
This variation in the weather (because of the direction of the Earth's axial tilt) results in the seasons.

Equator

equatorial planeThe Equator
The two instants when the Sun is directly overhead at the Equator are the equinoxes.
In the cycle of Earth's seasons, the equatorial plane runs through the Sun twice per year: on the equinoxes in March and September.

Solstice

solsticessummer solsticewinter solstice
In meteorological terms, the solstices (the maximum and minimum insolation) do not fall in the middles of summer and winter.
The seasons of the year are determined by reference to both the solstices and the equinoxes.

Wheel of the Year

SabbatMaboncross-quarter day
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 Wheel of the Year is an annual cycle of seasonal festivals, observed by many modern Pagans, consisting of the year's chief solar events (solstices and equinoxes) and the midpoints between them.

Effect of Sun angle on climate

sun angleannual coldangle of incidence
The low angle of Sun during the winter months means that incoming rays of solar radiation are spread over a larger area of the Earth's surface, so the light received is more indirect and of lower intensity.
The amount of heat energy received at any location on the globe is a direct effect of Sun angle on climate, as the angle at which sunlight strikes the Earth varies by location, time of day, and season due to the Earth's orbit around the Sun and the Earth's rotation around its tilted axis.

Sunlight

sunshinesolar radiationnatural light
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.
But the seasonal and latitudinal distribution and intensity of solar radiation received at Earth's surface does vary.

Daytime

dayday lengthdaytime hours
The effect of axial tilt is observable as the change in day length and altitude of the Sun at solar noon (the Sun's culmination) during the year.
Given that Earth's own axis of rotation is tilted 23.44° to the line perpendicular to its orbital plane, called the ecliptic, the length of daytime varies with the seasons on the planet's surface, depending on the observer's latitude.

Solar irradiance

solar radiationinsolationsolar insolation
In meteorological terms, the solstices (the maximum and minimum insolation) do not fall in the middles of summer and winter. 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.
Insolation is essential for numerical weather prediction and understanding seasons and climatic change.

Ocean current

currentscurrentocean currents
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.
In addition, the areas of surface ocean currents move somewhat with the seasons; this is most notable in equatorial currents.

Sharad

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).
Sharad is the early autumn season or ritu in the Hindu calendar.

Milankovitch cycles

Milankovitch cycleMilankovitch theoryMilankovich cycle
Over thousands of years, the Earth's axial tilt and orbital eccentricity vary (see Milankovitch cycles).
The combined effect is that proximity to the Sun occurs during different astronomical seasons.

Spring (season)

springspringtimespring season
In temperate and sub-polar regions, four seasons based on the Gregorian calendar are generally recognized: spring, summer, autumn or fall, and winter.
Spring, also known as springtime is one of the four temperate seasons, following winter and preceding summer.

Köppen climate classification

ClimateKöppenKöppen-Geiger climate classification system
The term aseasonal refers to the lack in the tropical zone of large differences in daylight hours and mean monthly (or daily) temperature throughout the year.

Apsis

perigeeperihelionapogee
In fact, Earth reaches perihelion (the point in its orbit closest to the Sun) in January, and it reaches aphelion (the point farthest from the Sun) in July, so the slight contribution of orbital eccentricity opposes the temperature trends of the seasons in the Northern Hemisphere.
However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earth's axis, which is 23.4 degrees away from perpendicular to the plane of Earth's orbit around the sun.

Horae

HoursSeasonsAuxo
In Greek mythology the Horae or Horai or Hours (Ὧραι, Hōrai, "Seasons") were the goddesses of the seasons and the natural portions of time.