Wednesday 18 June 2014
The sky is everything that lies a certain distance above the surface of the Earth, including the atmosphere and outer space. 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 conventionally divided into regions called constellations. Usually, the term sky is used from the point of view of the Earth's surface; however, the exact meaning of the term can vary. For example, in some cases the sky is defined as only the denser portions of the atmosphere. During daylight, the sky appears to be blue because air scatters blue sunlight more than it scatters red. At night, the sky appears to be a mostly dark surface or region scattered with stars. Source
