The sky is often defined as the place a person sees when he looks up from the earth. Although almost everyone have seen it, the sky is hard to be defined precisely. The concept of the sky, as it is applied here on earth, can be generalized to mean the space seen when one looks upward from the surface of any planet. The sky is also sometimes defined as the denser gaseous zone of a planet's atmosphere.
On earth, the sky usually looks blue on a sunny day, turns orange and red during sunrise and sunset, and becomes black at night. Some of the things people see in the sky are clouds, rainbows, and aurorae. Lightning can also be seen in the sky during storms. People also say that birds, airplanes, and kites fly in the sky.
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 travelling in. The celestial sphere is divided into regions called constellations. (See also Chinese constellation).
Sky gods/goddesses in different cultures: