The sky is considered everything that lies above the surface of the Earth, including the atmosphere and the outer space.
In astronomy, the sky is also known under the term “celestial sphere”. This is an abstract sphere, on which the Sun, Moon, planets, and stars appear to be drifting.
Most commonly, the term sky refers to a perspective from the Earth’s surface. However, the meaning and usage of the term can vary.
An observer on the Earth can only see a small part of the sky, which resembles a dome that appears flatter during the day than at night.
In some cases (such as when discussing the weather), the sky refers to only the lower layers of the atmosphere.