This article is about Earth's sky. For other skies, see extraterrestrial skies. For other uses, see Sky (disambiguation). The sky above the clouds The sky (or celestial dome) is everything that lies 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 abstract sphere, centred on the earth, on which the Sun, stars, planets, and the Moon appear to be traveling. The celestial sphere is conventionally divided into designated areas called constellations. Usually, the term sky is used informally