sky

1. The expanse of air over any given point on the earth; the upper atmosphere as seen from the earth's surface.
2. The appearance of the upper atmosphere, especially with reference to weather. Often used in the plural: Threatening skies portend a storm.
3. The celestial regions; the heavens: stars in the southern sky.
4. The highest level or degree: reaching for the sky.

1. To hit or throw (a ball, for example) high in the air.
2. To hang (a painting, for example) high up on the wall, above the line of vision.

[Middle English, from Old Norse skȳ, cloud.]

noun

The celestial regions as seen from the earth: air, firmament, heaven (often used in plural). Archaic welkin. See high/low.

verb

To rise abruptly and precipitously: rocket, skyrocket, soar. Informal shoot up. See increase/decrease.

Idioms beginning with sky:
sky's the limit, the

In addition to the idiom beginning with sky, also see blow sky-high; out of a clear blue sky; pie in the sky reach for the sky.

Definition: earth's atmosphere
Antonyms: earth

Quotes:

"The sky is the daily bread of the eyes." - Ralph Waldo Emerson

"And that inverted bowl we call The Sky, where under crawling coop't we live and die, lift not thy hands to It for help -- for it rolls impotently on as thou or I." - Omar Khayyam

"I never saw a man who looked with such a wistful eye upon that little tent of blue which prisoners call the sky." - Oscar Wilde

The sky usually signifies peace and freedom of expression when it is clear and blue. If cloudy and overcast, the sky may be forecasting sadness and trouble.

Please help improve this article by expanding it. Further information might be found on the talk page. (September 2009)

For other uses, see Sky (disambiguation).

Crepuscular rays of light shining through clouds near the Washington Monument in Washington D.C.

The sky is the part of the atmosphere or of outer space visible from the surface of any astronomical object. It is difficult to define precisely for several reasons. During daylight, the sky of Earth has the appearance of a deep blue surface because of the air's scattering of sunlight.^[1][2][3][4] The sky is sometimes defined as the denser gaseous zone of a planet's atmosphere. At night the sky has the appearance of a black surface or region scattered with stars.

During the day the Sun can be seen in the sky, unless covered by clouds. In the night sky (and to some extent during the day) the moon, planets and stars are visible in the sky. Some of the natural phenomena seen in the sky are clouds, rainbows, and aurorae. Lightning and precipitation can also be seen in the sky during storms. On Earth, birds, insects, aircraft, and kites are often considered to fly in the sky. As a result of human activities, smog during the day and light radiance during the night are often seen above large cities (see also light pollution).

In the field of astronomy, the sky is also called the celestial sphere. This is an imaginary dome where the sun, stars, planets, and the moon are seen to be traveling. The celestial sphere is divided into regions called constellations.

See skies of other planets for descriptions of the skies of various planets and moons in the solar system.

Contents 1 Sky luminance and colors 2 See also 3 Gallery 4 References 5 External links

Sky luminance and colors

Clouds made orange by a sunset

When seen from altitude, as here from an airplane, the sky's color varies from pale to dark at elevations approaching the zenith

Light from the sky is a result of the scattering of sunlight, which results in a blue color perceived by the human eye. On a sunny day Rayleigh scattering gives the sky a blue gradient — dark in the zenith, light near the horizon. Light that comes in from overhead encounters 1/38th of the air mass that light coming along a horizon path encounters. So, fewer particles scatter the zenith sunbeam, and therefore the light remains a darker blue.^[5]The blueness is at the horizon because the blue light coming from great distances is also preferentially scattered. This results in a red shift of the far lightsources that is compensated by the blue hue of the scattered light in the line of sight. In other words some of the red light scatters also and if it does at a point at a great distance from the observer it has a much higher chance of reaching the observer than blue light. At distances nearing infinity the scattered light is therefore white. Far away clouds or snowy mountaintops will seem yellow for that reason; that effect is not obvious on clear days, but very pronounced when clouds are covering the line of sight reducing the blue hue from scattered sunlight. This can be observed at the bottom part of the picture on top of the article.

Another thing worth mentioning is that the scattering due to very small particles (molecule sized) is almost random. The scattering in a 90 degree angle is still half of the scattering that reflects or goes forward. This causes the blue sky to be almost evenly colored and thin clouds to form a white area around the sun, because the big particles the clouds are made of are scattering preferentially only at low angles. The color of the clouds is also due to scattering and a cloud at a small distance has the white color because all the light from these clouds is scattered multiple times in the mass of particles and no wavelenght effects will be observed.

The sky can turn a multitude of colors such as red, orange, purple and yellow (especially near sunset or sunrise) and black at night. Scattering effects also partially polarize light from the sky, most pronounced at an angle 90° from the sun.

Sky luminance distribution models have been recommended by the International Commission on Illumination (CIE) for the design of daylighting schemes. Recent developments relate to “all sky models” for modelling sky luminance under weather conditions ranging from clear sky to overcast.^[6]

See also

• Air
• Diffuse sky radiation
• Rayleigh scattering
• Sky brightness
• Skygazing
• Sunlight
• Extraterrestrial skies

Gallery

Turbulent skies

The sky's zenith appears centered in this daytime photograph taken looking up though trees

References

1. ^ Tyndall, John (December 1868). "On the Blue Colour of the Sky, the Polarization of Skylight, and on the Polarization of Light by Cloudy Matter Generally". Proceedings of the Royal Society of London 17: pp. 223–233. doi:10.1098/rspl.1868.0033. http://links.jstor.org/sici?sici=0370-1662%281868%2F1869%2917%3C223%3AOTBCOT%3E2.0.CO%3B2-X&size=LARGE. 
2. ^ Rayleigh, Lord (June 1871). "On the scattering of light by small particles". Philosophical Magazine 41, 275: pp. 447–451. 
3. ^ Watson, JG (June 2002). "Visibility: Science and Regulation". J. Air & Waste Manage. Assoc 52: pp. 628–713. http://scholar.google.com/scholar?hl=en&lr=&q=cache:aulPiqN6uTUJ:www.awma.org/journal/pdfs/2002/6/Crit_Review.pdf+. Retrieved 2007-04-19. 
4. ^ Why is the sky Blue?
5. ^ Why is the sky bluer on top than at the horizon
6. ^ eSim 2008 (May 20th - 22nd, 2008) General Sky Standard Defining Luminance DistributionsPDF (710 KiB)

External links

Wikimedia Commons has media related to: Sky

• Day sky images
• Night Sky images
• Sky photo gallery
• Why is the sky blue?

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - himmel, himmelstrøg
v. tr. - skyde højt op i luften, hænge højt

idioms:

• sky blue    himmelblå
• the sky is the limit    der er ingen grænser

Nederlands (Dutch)
hemel, lucht

Français (French)
n. - ciel
v. tr. - (Sport) faire une chandelle (balle)

idioms:

• sky blue    bleu ciel
• the sky is the limit    tout va (excl)

Deutsch (German)
n. - Himmel
v. - hochwerfen

idioms:

• sky blue    Himmelblau
• the sky is the limit    dem Erfolg sind keine Grenzen gesetzt

Ελληνική (Greek)
n. - ουρανός
v. - εκθέτω (πίνακες κ.λπ.) σε ύψος πάνω από το κεφάλι

idioms:

• sky blue    γαλανός, γαλάζιος, ουρανής
• the sky is the limit    όσο τραβάει η ψυχή σου!, κανένα όριο!

Italiano (Italian)
cielo

idioms:

• sky blue    azzurro cielo
• the sky is the limit    senza badare al prezzo, senza limiti

Português (Portuguese)
n. - atmosfera (f)
v. - atirar para cima, pendurar quadro demasiadamente alto na parede

idioms:

• sky blue    azul celeste
• the sky is the limit    o céu (m) é o limite

Русский (Russian)
небо, погода, вешать (картину высоко) на стене, подбросить в воздух, высоко бросать

idioms:

• sky blue    лазурь, водянистое молоко
• the sky is the limit    нет предела, неограниченно

Español (Spanish)
n. - cielo
v. tr. - colgar un cuadro alto en la pared, por encima de la línea visual

idioms:

• sky blue    celeste, azul celeste
• the sky is the limit    ¡todo es posible!, no hay límite

Svenska (Swedish)
n. - himmel, sky
v. - slå högt upp i luften, hänga högt upp på väggen

中文（简体）(Chinese (Simplified))
天空, 天堂, 天色, 击向空中, 挂在高处

idioms:

• sky blue    天蓝色, 淡蓝色
• the sky is the limit    没有限制

中文（繁體）(Chinese (Traditional))
n. - 天空, 天堂, 天色
v. tr. - 擊向空中, 掛在高處

idioms:

• sky blue    天藍色, 淡藍色
• the sky is the limit    沒有限制

한국어 (Korean)
n. - 하늘, 기후, (제복 입은) 경관
v. tr. - 높은 곳에 걸다, 높이 쳐 올리다

idioms:

• the sky is the limit    무제한이다, 기회는 얼마든지 있다, (내기에) 얼마든지 걸겠다

日本語 (Japanese)
n. - 空, 天気, 気候, 風土, 天国, 天, 上空, 天空

idioms:

• sky blue    空色, スカイブルー
• the sky is the limit    無制限

العربيه (Arabic)
‏(الاسم) ألسماء (فعل) يقذف ألكرة عاليا, يعلق لوحه زيتيه فوق خط ألبصر‏

עברית (Hebrew)
n. - ‮שמיים, רקיע, אקלים‬
v. tr. - ‮חבט (בכדור) אל על, בעט לשחקים‬

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