Other Free Encyclopedias » Science Encyclopedia » Science & Philosophy: Jean-Paul Sartre Biography to Seminiferous tubules

Seasons

earth sun summer winter

Seasons on Earth are found only in the temperate zones. These zones extend from 23.5° north (and south) latitude to 66.5° north (and south) latitude. In these regions of Earth nature exhibits four seasons; spring, summer, autumn (or fall) and winter. Each season is characterized by differences in temperature, amounts of precipitation, and the length of daylight. Spring comes from an Old English word meaning to rise. Summer originated as a Sanskrit word meaning half year or season. Autumn comes originally from a Etruscan word for maturing. Winter comes from an Old English word meaning wet or water. The equatorial regions or torrid zones have no appreciable seasonal changes and here one generally finds only a wet season and a dry season. In the polar regions we have only a light season and a dark season.

In the Northern Hemisphere, astronomers assign an arbitrary starting date for each season. Spring begins around March 21 and summer begins around June 21. Autumn begins around September 23 and winter around December 21. Because every fourth year is a leap year and February then has 29 days, the dates of these seasonal starting points change slightly. In the Southern Hemisphere the seasons are reversed with spring beginning in September, summer in December, fall in March, and winter in June. Seasons in the Southern Hemisphere are generally milder due to the moderating presence of larger amounts of ocean surface as compared to the Northern Hemisphere.

Changes in the seasons are caused by Earth's movement around the Sun. Because Earth orbits the Sun at The seasons. Illustration by Hans & Cassidy. Courtesy of Gale Group. varying distances, many people think that the seasons result from the changes in the Earth-Sun distance. This belief is incorrect. In fact, Earth is actually closer to the Sun in January compared to June by approximately three million miles.

Earth makes one complete revolution about the Sun each year. The reason for the seasons is that the axis of Earth's rotation is tilted with respect to the plane of its orbit. This tilt, called the obliquity of Earth's axis, is 23.5degrees from a line drawn perpendicular to the plane of Earth's orbit. As Earth orbits the Sun, there are times of the year when the North Pole is alternately tilted toward the Sun (during northern hemispheric summer) or tilted away from the Sun (during northern hemispheric winter). At other times the axis is generally parallel to the incoming Sun's rays. During summer, two effects contribute to produce warmer weather. First, the Sun's rays fall more directly on Earth's surface and this results in a stronger heating effect. The second reason for the seasonal temperature differences results from the differences in the amount of daylight hours versus nighttime hours. The Sun's rays warm Earth during daylight hours and Earth cools at night by re-radiating heat back into space. This is the major reason for the warmer days of summer and cooler days of winter. The orientation of Earth's axis during summer results in longer periods of daylight and shorter periods of darkness at this time of year. At the mid-northerly latitudes summer days have about 16 hours of warming daylight and only eight hours of cooling nights. During mid-winter the pattern is reversed and we have longer nights and shorter days. To demonstrate that it is the daylight versus darkness ratio that produces climates that make growing seasons possible, one should note that even in regions only 30° from the poles one finds plants such as wheat, corn, and potatoes growing. In these regions the Sun is never very high in the sky but because of the orientation of Earth's axis, the Sun remains above the horizon for periods for over 20 hours a day from late spring to late summer.

Astronomers have assigned names to the dates at which the official seasons begin. When the axis of Earth is perfectly parallel to the incoming Sun's rays in spring the Sun stands directly over the equator at noon. As a result, daylight hours equal night time hours everywhere on Earth. This gives rise to the name given to this date, the vernal equinox. Vernal refers to spring and the word equinox means equal night. On the first day of fall, the autumnal equinox also produces 12 hours of daylight and 12 hours of darkness everywhere on Earth.

The name given for the first day of summer results from the observation that as the days get longer during the spring, the Sun's height over its noon horizon increases until it reaches June 21. Then on successive days it dips lower in the sky as Earth moves toward the autumn and winter seasons. This gives rise to the name for that date, the Summer Solstice, because it is as though the Sun "stands still" in its noon height above the horizon. The Winter Solstice is likewise named because on December 21 the sun reaches the lowest noon time height and appears to "stand still" on that date as well.

In the past, early humans celebrated the changes in the seasons on some of these cardinal dates. The vernal equinox was a day of celebration for the early Celtic tribes in ancient Britain, France, and Ireland. Other northern European tribes also marked the return of warmer weather on this date. Even the winter solstice was a time to celebrate, as it marked the lengthening days that would lead to spring. The ancient Romans celebrated the Feast of Saturnalia on the winter solstice. And even though there are no historical records to support the choice of a late December date for the birth of Christ, Christians in the fourth century A.D. chose to celebrate his birth on the winter solstice. In the Julian calendar system in use at that time this date fell on December 25.

See also Global climate.


Resources

Books

Abell, George, David Morrison, and Sydney Wolff. Exploration of the Universe. 6th ed. Philadelphia: Saunders, 1993.

Bacon, Dennis Henry, and Percy Seymour. A Mechanical History of the Universe. London: Philip Wilson Publishing, Ltd., 2003.

Hartman, William. The Cosmic Voyage. Belmont, CA: Wadsworth, 1992.

Pasachoff, Jay. Astronomy: From the Earth to the Universe. 4th ed. Philadelphia: Saunders, 1991.


Darrel B. Hoff

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Autumnal equinox

—The date in the fall of the year when Earth experiences 12 hours of daylight and 12 hours of darkness, usually about September 23rd.

Obliquity

—The amount of tilt of Earth's axis. This tilt is equal to 23.5 degrees drawn from a line perpendicular to the orbit of Earth.

Summer solstice

—The date on which the Sun is highest in the sky at noon, usually about June 21st.

Temperate zones

—The two regions on Earth bounded by the 23.5 degree latitude and the 66.5 degree latitude.

Torrid zone

—A zone on Earth bounded by 23.5 degrees North and South Latitude.

Vernal Equinox

—The intersection of the celestial equator and ecliptic which the Sun appears to reach on or about March 21.

Winter solstice

—The date on which the Sun's noontime height is at its lowest, usually on December 21st.

[back] Seasonal Winds

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

almost 2 years ago

Thanks for more information about visit this link:
http://www.adword.co.in/packers-and-movers-hyderabad/
http://www.adword.co.in/packers-and-movers-mumbai/
http://www.adword.co.in/packers-and-movers-pune/

Vote down Vote up

almost 7 years ago

Your information on the astronomical seasons may be accurate and factual within certain parameters. Your article makes some acknowlegement that real seasonal changes don't always exactly follow the astronomical dates. Still, I find your article quite biased in favour of astronomical reckoning if for no other reason than the fact it's the only method you ever refer to.

Essentially you make no reference to the equally 'official' climatological seasons established by the World Meteorological Organization. In the northern hemisphere, spring officially starts on March 1, summer on June 1, autumn on September 1, and winter on December 1. Climatological statistics indicate that in most temperate regions, these dates more closely match the real changes in season than the astronomical dates.

Your article also ignores a six season model adopted by many ecologists. Along with the traditional four seasons, this reckoning additionally includes a pre-spring thaw season in between winter and the spring growing season, as well as a late summer serotinal season which marks a transtion between the estival 'high summer' and the autumnal season. A cited Wikipedia article entitled 'Season' has the only truly unbiased article I've ever seen about this complex subject (that nearly all other articles try to oversimplify). Wikipedia outlines the astronomical, climatological, and ecological seasons without favouring one reckoning over another.

I think it would be a step forward if all articles about this subject discussed all three methods of reckoning seasonal change rather than just the narrow one-size-fits-all approach used by astronomers.

Vote down Vote up

over 1 year ago

Packers and Movers Hyderabad @
http://packersandmovershyderabad.top3rd.co.in
Packers and Movers Bangalore @
http://packersandmoversbangalore.top3rd.co.in
Packers and Movers Pune @
http://packersandmoverspune.top3rd.co.in
Packers and Movers Mumbai @
http://packersandmoversmumbai.top3rd.co.in
Packers and Movers Chennai @
http://packersandmoverschennai.top3rd.co.in
Packers and Movers Delhi @
http://packersandmoversdelhi.top3rd.co.in

Vote down Vote up

over 1 year ago


Packers and Movers Hyderabad @
http://ipackersmovershyderabad.top4th.in
Packers and Movers Bangalore @
http://ipackersmoversbangalore.top4th.in
Packers and Movers Pune @
http://ipackersmoverspune.top4th.in
Packers and Movers Mumbai @
http://ipackersmoversmumbai.top4th.in
Packers and Movers Chennai @
http://ipackersmoverschennai.top4th.in
Packers and Movers Delhi @
http://ipackersmoversdelhi.top4th.in
Packers and Movers Gurgaon @
http://ipackersmoversgurgaon.top4th.in

Vote down Vote up

over 1 year ago


Packers and Movers Hyderabad @
http://packersmovershyderabad.top3rd.in
Packers and Movers Bangalore @
http://packersmoversbangalore.top3rd.in
Packers and Movers Pune @
http://packersmoverspune.top3rd.in
Packers and Movers Mumbai @
http://packersmoversmumbai.top3rd.in
Packers and Movers Chennai @
http://packersmoverschennai.top3rd.in
Packers and Movers Delhi @
http://packersmoversdelhi.top3rd.in
Packers and Movers Gurgaon @
http://packersmoversgurgaon.top3rd.in

Vote down Vote up

over 1 year ago


Packers and Movers Hyderabad @
http://packersmovershyderabad.top3rd.in
Packers and Movers Bangalore @
http://packersmoversbangalore.top3rd.in
Packers and Movers Pune @
http://packersmoverspune.top3rd.in
Packers and Movers Mumbai @
http://packersmoversmumbai.top3rd.in
Packers and Movers Chennai @
http://packersmoverschennai.top3rd.in
Packers and Movers Delhi @
http://packersmoversdelhi.top3rd.in
Packers and Movers Gurgaon @
http://packersmoversgurgaon.top3rd.in

Vote down Vote up

almost 2 years ago

Thanks for more information about visit this link:
http://www.adword.co.in/packers-and-movers-bangalore/
http://www.adword.co.in/packers-and-movers-delhi/
http://www.adword.co.in/packers-and-movers-gurgaon/
http://www.adword.co.in/

Vote down Vote up

almost 2 years ago

Thanks for mour information visit:
http://top3th.co.in/packers-and-movers-gurgaon/
http://top3th.co.in/packers-and-movers-delhi/
http://top3th.co.in/packers-and-movers-navi-mumbai/
http://top3th.co.in/packers-and-movers-thane/
http://top3th.co.in/

Vote down Vote up

almost 2 years ago

Thanks More for information Visit:
http://www.export5th.in/packers-and-movers-in-gurgaon/
http://www.export5th.in/packers-and-movers-in-delhi/
http://www.export5th.in/packers-and-movers-in-noida/
http://www.export5th.in/packers-and-movers-in-chennai/
http://www.export5th.in/packers-and-movers-in-dwarka/
http://www.export5th.in/packers-and-movers-in-ghaziabad/
http://www.export5th.in/packers-and-movers-in-faridabad/

Vote down Vote up

almost 2 years ago

Thanks for More information provide Top 3th Packers and Movers services
http://3th.co.in/packers-and-movers-delhi/
http://3th.co.in/packers-and-movers-noida/
http://3th.co.in/packers-and-movers-faridabad/
http://3th.co.in/packers-and-movers-ghaziabad/

Vote down Vote up

almost 2 years ago

Thanks for More information provide Export5th in packing & moving services at best shifting
http://www.export5th.in/packers-and-movers-in-bangalore/
http://www.export5th.in/packers-and-movers-in-hyderabad/
http://www.export5th.in/packers-and-movers-in-pune/
http://www.export5th.in/packers-and-movers-in-mumbai/

Vote down Vote up

over 2 years ago

Crystal X Mengatasi Keputihan
http://www.crystalxmengatasikeputihan.com
Keunggulan Produk Herbal Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/keunggulan-dari-crystal-x.html
Crystal X
http://distributor-resmi-nasa.blogspot.com/2013/05/manfaat-dan-bahaya-crystal-x.html
CRYSTAL X UNTUK PROGRAM HAMIL
http://www.crystalxmengatasikeputihan.com/2015/04/crystal-x-untuk-program-hamil-istri.html
Produk Terapi Untuk Suami Agar Istri Cepat Hamil
http://www.crystalxmengatasikeputihan.com/2015/04/produk-terapi-untuk-suami-agar-istri-cepat-hamil.html
Cara Pemesanan Produk Crytal X
http://www.crystalxmengatasikeputihan.com/p/blog-page.html
Cara Pemakaian Crystal X untuk Hasil Memuaskan
http://www.crystalxmengatasikeputihan.com/2015/04/cara-pemakaian-crystal-x-untuk-hasil.html
Crystal X Benar-Benar Aman
http://www.crystalxmengatasikeputihan.com/2015/04/apakah-crystal-x-benar-benar-aman_22.html
Khasiat Crystal X Merawat Organ Intim
http://www.crystalxmengatasikeputihan.com/2015/04/khasiat-crystal-x-merawat-organ-intim.html
Mengatasi Keputihan Dengan Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/mengatasi-keputihan-dengan-crystal-x.html
Peranan Crystal X Sebagai Pembunuh Bakteri Jahat
http://www.crystalxmengatasikeputihan.com/2015/04/peranan-crystal-x-sebagai-pembunuh.html
Fungsi Crystal X Untuk Memperlancar Menstruasi
http://www.crystalxmengatasikeputihan.com/2015/04/fungsi-crystal-x-untuk-memperlancar.html
Efek Samping Penggunaan Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/efek-samping-penggunaan-crystal-x.html
Mengatasi Keputihan Dengan Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/mengatasi-keputihan-dengan-crystal-x.html
Cara Mengatasi Keputihan Tanpa Efek Samping
http://www.crystalxmengatasikeputihan.com/2015/05/cara-mengatasi-keputihan-tanpa-efek.html

Vote down Vote up

over 2 years ago

Crystal X Mengatasi Keputihan
http://www.crystalxmengatasikeputihan.com
Keunggulan Produk Herbal Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/keunggulan-dari-crystal-x.html
Crystal X
http://distributor-resmi-nasa.blogspot.com/2013/05/manfaat-dan-bahaya-crystal-x.html
CRYSTAL X UNTUK PROGRAM HAMIL
http://www.crystalxmengatasikeputihan.com/2015/04/crystal-x-untuk-program-hamil-istri.html
Produk Terapi Untuk Suami Agar Istri Cepat Hamil
http://www.crystalxmengatasikeputihan.com/2015/04/produk-terapi-untuk-suami-agar-istri-cepat-hamil.html
Cara Pemesanan Produk Crytal X
http://www.crystalxmengatasikeputihan.com/p/blog-page.html
Cara Pemakaian Crystal X untuk Hasil Memuaskan
http://www.crystalxmengatasikeputihan.com/2015/04/cara-pemakaian-crystal-x-untuk-hasil.html
Crystal X Benar-Benar Aman
http://www.crystalxmengatasikeputihan.com/2015/04/apakah-crystal-x-benar-benar-aman_22.html
Khasiat Crystal X Merawat Organ Intim
http://www.crystalxmengatasikeputihan.com/2015/04/khasiat-crystal-x-merawat-organ-intim.html
Mengatasi Keputihan Dengan Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/mengatasi-keputihan-dengan-crystal-x.html
Peranan Crystal X Sebagai Pembunuh Bakteri Jahat
http://www.crystalxmengatasikeputihan.com/2015/04/peranan-crystal-x-sebagai-pembunuh.html
Fungsi Crystal X Untuk Memperlancar Menstruasi
http://www.crystalxmengatasikeputihan.com/2015/04/fungsi-crystal-x-untuk-memperlancar.html
Efek Samping Penggunaan Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/efek-samping-penggunaan-crystal-x.html
Mengatasi Keputihan Dengan Crystal X
http://www.crystalxmengatasikeputihan.com/2015/04/mengatasi-keputihan-dengan-crystal-x.html
Cara Mengatasi Keputihan Tanpa Efek Samping
http://www.crystalxmengatasikeputihan.com/2015/05/cara-mengatasi-keputihan-tanpa-efek.html

Vote down Vote up

over 3 years ago

Don't forget that the East Asian and Celtic seasonal calendars classify the solstices and equinoxes as the *midpoints* of their respective seasons rather than the starting points. That system puts the seasonal cusps at the four "cross-quarters" on February 3/4, May 5/6, August 6/7 and November 6/7.

Vote down Vote up

over 3 years ago

Don't forget to mention that the official "astronomical" definition of the four seasonal cusps is somewhat arbitrary and tends to over-compensate for seasonal temperature lag in most midlatitude climates. The coldest and hottest times of year are generally 1-2 weeks BEFORE the February and August cross-quarters, and the November cross-quarter (midpoint of "spring") is colder than the May cross-quarter (midpoint of "autumn").