Sky
Context
The region of the atmosphere and outer space seen from the earth
Explanation
The sky is the expanse that lies above the surface of the Earth, including the atmosphere and outer space, and is observed as a blue dome during the day and a starlit expanse at night.
Applications
The sky was clear and blue, with no clouds in sight.
Birds flying across the sky can be a relaxing sight.
Astronomers study the night sky to learn about stars and galaxies.