A season is a period of the year that is distinguished by special climate conditions. The four seasons—spring, summer, fall, and winter—follow one another regularly. Each has its own light, temperature, and weather patterns that repeat yearly.

In the Northern Hemisphere, winter generally begins on December 21 or 22. This is the winter solstice, the day of the year with the shortest period of daylight. Summer begins on June 20 or 21, the summer solstice, which has the most daylight of any day in the year. Spring and fall, or autumn, begin on equinoxes, days that have equal amounts of daylight and darkness. The vernal, or spring, equinox falls on March 20 or 21, and the autumnal equinox is on September 22 or 23.

The seasons in the Northern Hemisphere are the opposite of those in the Southern Hemisphere. This means that in Argentina and Australia, winter begins in June. The winter solstice in the Southern Hemisphere is June 20 or 21, while the summer solstice, the longest day of the year, is December 21 or 22.

Seasons occur because Earth is tilted on its axis relative to the orbital plane, the invisible, flat disc where most objects in the solar system orbit the sun. Earth’s axis is an invisible line that runs through its center, from pole to pole. Earth rotates around its axis.

In June, when the Northern Hemisphere is tilted toward the sun, the sun’s rays hit it for a greater part of the day than in winter. This means it gets more hours of daylight. In December, when the Northern Hemisphere is tilted away from the sun, with fewer hours of daylight.

Seasons have an enormous influence on vegetation and plant growth. Winter typically has cold weather, little daylight, and limited plant growth. In spring, plants sprout, tree leaves unfurl, and flowers blossom. Summer is the warmest time of the year and has the most daylight, so plants grow quickly. In autumn, temperatures drop, and many trees lose their leaves.

The four-season year is typical only in the mid-latitudes. The mid-latitudes are places that are neither near the poles nor near the Equator. The farther north you go, the bigger the differences in the seasons. Helsinki, Finland, sees 18.5 hours of daylight in the middle of June. In mid-December, however, it is light for less than 6 hours. Athens, Greece, in southern Europe, has a smaller variation. It has 14.5 hours of daylight in June and 9.5 hours in December.

Places near the Equator experience little seasonal variation. They have about the same amount of daylight and darkness throughout the year. These places remain warm year-round. Near the Equator, regions typically have alternating rainy and dry seasons.

Polar regions experience seasonal variation, although they are generally colder than other places on Earth. Near the poles, the amount of daylight changes dramatically between summer and winter. In Barrow, Alaska, the northernmost city in the U.S., it stays light all day long between mid-May and early August. The city is in total darkness between mid-November and January.

season
Seasons are determined by the Earth's exposure to the sun.

Seasons in Alaska
Sometimes, seasons are determined by both natural and man-made activity. In the U.S. state of Alaska, people like to say there are three seasons: "winter, still winter, and construction season."

Ritu
A ritu is a season in the traditional Hindu calendar, used in parts of India. There are six ritu: vasanta (spring); grishma (summer); varsha (rainy or monsoon); sharat (autumn); hemant (pre-winter); and shishira (winter).

'Tis the Season
The word 'season' can be used to signify a time of year when an activity or process is allowed to happen. Seasons can be natural, like hurricane season, which is the time of year when hurricanes are most likely to develop. Seasons can also be artificially created, like hunting season, which is the time of year a community allows people to hunt certain wild animals.

Meteorological Seasons
Meteorologists, scientists who study the weather, divide each of the seasons into three whole months. Spring begins March 1, summer June 1, autumn September 1, and winter December 1.

alternate
Verb

to switch back and forth.

autumnal equinox
Noun

autumn day, usually around September 22, when day and night are of generally equal length.

Noun

an invisible line around which an object spins.

blossom
Verb

to bloom or thrive.

Noun

all weather conditions for a given location over a period of time.

distinguish
Verb

to differentiate or recognize as different.

dry season
Noun

time of year with little precipitation.

Noun

imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude.

flower
Noun

blossom or reproductive organs of a plant.

grishma
Noun

summer season in the Hindu calendar.

hemanta
Noun

pre-winter season in the Hindu calendar. Also called hemant.

Hindu
Noun

religion of the Indian subcontinent with many different sub-types, most based around the idea of "daily morality."

Noun

line where the Earth and the sky seem to meet.

hunting season
Noun

time of the year when hunting certain wild animals is allowed by law.

hurricane season
Noun

time of year when the risk of hurricanes is greatest. Atlantic hurricane season runs from June 1 to November 30.

meteorologist
Noun

person who studies patterns and changes in Earth's atmosphere.

midlatitudes
Noun

geographic regions between the Equator and the poles.

Noun

seasonal change in the direction of the prevailing winds of a region. Monsoon usually refers to the winds of the Indian Ocean and South Asia, which often bring heavy rains.

Northern Hemisphere
Noun

half of the Earth between the North Pole and the Equator.

pole
Noun

extreme north or south point of the Earth's axis.

rainy season
Noun

time of year when most of the rain in a region falls.

Noun

period of the year distinguished by special climatic conditions.

seasonal variation
Noun

differences in temperature, climate, and weather between seasons of the year.

sharat
Noun

autumn or fall season in the Hindu calendar.

shishira
Noun

winter season in the Hindu calendar.

Southern Hemisphere
Noun

half of the Earth between the South Pole and the Equator.

sprout
Verb

to begin to grow.

summer
Noun

time of year when part of the Earth receives the most daylight: The months of June, July, and August in the Northern Hemisphere and the months of December, January, and February in the Southern Hemisphere.

summer solstice
Noun

day of the year with the most hours of sunlight, June 20 or 21 in the Northern Hemisphere and December 21 or 22 in the Southern Hemisphere.

sun
Noun

star at the center of our solar system.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

tilt
Verb

to lean or slant.

unfurl
Verb

to uncurl or straighten out.

varsha
Noun

rainy or monsoon season in the Hindu calendar.

vasanta
Noun

spring season in the Hindu calendar.

vernal equinox
Noun

day, usually around March 21, when day and night are of generally equal length. Also called the spring equinox.

Noun

state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

winter
Noun

time of year when part of the Earth receives the least daylight: December, January, and February in the Northern Hemisphere and June, July, and August in the Southern Hemisphere.

winter solstice
Noun

(December 22 in the Northern Hemisphere, June 22 in the Southern Hemisphere) longest night of the year and the beginning of winter.