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

Turbulent skies

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

Clouds made orange by a sunset

The sky is the part of the atmosphere or of outer space visible from the surface of any astronomical object. Altitude is the Elevation of a point or object from a known level or datum (plural data Overview Fixed-wing aircraft range from small training and recreational aircraft to Wide-body aircraft and military cargo aircraft. In broad terms the zenith is the direction pointing directly above a particular location ( Perpendicular, Orthogonal) A tree is a perennial Woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or The colour orange occurs An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. s are significant physical entities, associations or structures which current Science has confirmed to exist in Space. It is difficult to define precisely for several reasons. During daylight the sky of Earth has the appearance of a deep blue surface, as the result of the air's scattering of sunlight. Daylight or the light of day is the combination of all direct and indirect Sunlight outdoors during the daytime (and perhaps Twilight) EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Blue is a Colour, the Perception of which is evoked by Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Scattering is a general physical process whereby some forms of Radiation, such as Light, Sound or moving particles for example are forced to deviate from Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. ^[1][2][3][4] The sky is sometimes defined as the denser gaseous zone of a planet's atmosphere. This page is about the physical properties of gas as a state of matter A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " At night the sky has the appearance of a black surface or region scattered with stars. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth

During the day the Sun can be seen in the sky, unless covered by clouds. The Sun (Sol is the Star at the center of the Solar System. A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body In the night sky (and to some extent during the day) the moon, planets and stars are visible in the sky. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth Some of the natural phenomena seen in the sky are clouds, rainbows, and aurorae. Nature, in the broadest sense is equivalent to the natural world, physical universe, material world or material universe. A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body A rainbow is an optical and meteorological phenomenon that causes a spectrum of Light to appear in the Sky when the Sun Lightning and precipitation can also be seen in the sky during storms. Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface and strongly implying Severe weather. On Earth, birds, insects, aircraft, and kites are often considered to fly in the sky. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described A kite is a flying tethered object that depends upon the tension of a tethering system Flight is the process by which an object achieves sustained movement either through the Air (or movement beyond Earth's atmosphere, in the case of 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). Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus Smog is a kind of Air pollution; the word "smog" is a Portmanteau of Smoke and Fog. A city is an Urban area with a large Population and a particular Administrative, Legal, or Historical status Light pollution, also known as photopollution or luminous pollution, is excess or obtrusive Light created mainly by Humans Among other effects

In the field of astronomy, the sky is also called the celestial sphere. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius " This is an imaginary dome where the sun, stars, planets, and the moon are seen to be travelling. The Sun (Sol is the Star at the center of the Solar System. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is The celestial sphere is divided into regions called constellations. In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture

See skies of other planets for descriptions of the skies of various planets and moons in the solar system. The ' Sky ' of a world refers to the view of the heavens from its surface The Solar System consists of the Sun and those celestial objects bound to it by Gravity.

Sky luminance and colors

The light from the sky is a result of the scattering of sunlight, which results in a light blue color perceived by the human eye. Diffuse sky radiation is Solar radiation reaching the Earth 's surface after having been scattered from the direct solar beam by Molecules On a sunny day Rayleigh Scattering gives the sky a blue gradient — dark in the zenith, light near the horizon. Rayleigh scattering (named after Lord Rayleigh) is the elastic Scattering of Light or other electromagnetic radiation by particles much smaller In Graphics software for Digital image editing, the term gradient is used for a gradual blend of colour which can be considered as an even gradation In broad terms the zenith is the direction pointing directly above a particular location ( Perpendicular, Orthogonal) The horizon ( Ancient Greek ὁ ὁρίζων, /ho horídzôn/ from ὁρίζειν, "to limit" is the apparent line that separates Light that comes in from overhead encounters an air mass 1/38th of the mass that of a sunbeam coming along a horizon paths. So, fewer particles scatter the zenith sunbeam, and, therefore the light remains a darker blue. ^[5]

The sky can turn a multitude of colors such as red, orange and yellow (especially near sunset or sunrise) and black at night. Sunset, also called sundown in some American English Dialects is the instant when the trailing edge of the Sun 's disk disappears below Sunrise is the instant at which the upper edge of the Sun appears above the Horizon in the East. Night or nighttime is the period of Time when the Sun is below the Horizon. Scattering effects also partially polarize light from the sky. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations

Sky luminance distribution models have been recommended by the International Commission on Illumination (CIE) for the design of daylighting schemes. Luminance is a photometric measure of the density of Luminous intensity in a given direction Established in 1913 and based in Vienna, Austria, the International Commission on Illumination (usually known as the CIE for its French name Commission Daylighting is the practice of placing Windows or other transparent media and reflective surfaces so that during the day natural light provides effective internal illumination Recent developments relate to “all sky models” for modelling sky luminance under weather conditions ranging from clear sky to overcast. Luminance is a photometric measure of the density of Luminous intensity in a given direction The weather is a set of all the phenomena occurring in a given Atmosphere at a given Time. Overcast or overcast weather is the meteorological condition in which Clouds obscure 95% or more of the sky ^[6]

Dark Skies

Dark Skies is the name usually given to the campaign to reduce and eventually eliminate light pollution from as much of the planet as possible. Light pollution, also known as photopollution or luminous pollution, is excess or obtrusive Light created mainly by Humans Among other effects The campaign is led by the International Dark Sky Association (IDA) and supported by organizations in many countries such as The Royal Astronomical Society of New Zealand - RASNZ and Dark Sky Taonga. Light pollution is defined by the IDA as; "Any adverse effect of artificial light including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste.

See also

• Air
• Diffuse sky radiation — Why the sky is blue. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Diffuse sky radiation is Solar radiation reaching the Earth 's surface after having been scattered from the direct solar beam by Molecules
• Sky brightness
• Skygazing

References

1. ^ Tyndall, John (December 1868). This article is primarily about the brightness of the night sky Skygazing is the act of observing the Sky for pleasure or with an astronomical interest John Tyndall FRS ( August 2, 1820 &ndash December 4, 1893) was a prominent 19th century Irish Physicist. "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. Proceedings of the Royal Society is the parent title of two Scientific journals published by the Royal Society. 223-233.  
2. ^ Rayleigh, Lord (June 1871). John William Strutt 3rd Baron Rayleigh OM (12 November 1842 &ndash 30 June 1919 was an English Physicist who with William Ramsay, discovered "On the scattering of light by small particles". Philosophical Magazine 41, 275: pp. The Philosophical Magazine is arguably the world’s oldest commercially published Scientific journal. 447-451.  
3. ^ Watson, JG (June 2002). "Visibility: Science and Regulation". J. Air & Waste Manage. Assoc 52: pp. 628-713.  
4. ^ Why is the sky Blue?
5. ^ Why is the sky bluer on top than at the horizon
6. ^ CIE General Sky Standard Defining Luminance DistributionsPDF (710 KiB)

External links

• Day Sky Images
• Night Sky Images
• Sky Photo Gallery
• Why is the sky blue?

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