The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space.
In the aerospace context, the sky refers to the atmosphere and the celestial space above the surface of the Earth. It is the domain in which airplanes and other aircraft operate, and it is also the domain in which satellites and other spacecraft orbit. Some examples of activities that take place in the sky in the aerospace context include:
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Air travel: Commercial airplanes, private planes, and other aircraft fly through the sky to transport people and cargo from one location to another.
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Space exploration: Satellites and other spacecraft are launched into orbit around the Earth or other celestial bodies, where they perform a variety of tasks such as communication, observation, and navigation.
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Military operations: Military aircraft, including fighters, bombers, and transport planes, operate in the sky to perform a variety of tasks such as surveillance, transportation, and combat.
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Aerial surveys: Aircraft are used to conduct aerial surveys of the Earth's surface for a variety of purposes, including mapping, environmental monitoring, and resource exploration.
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Skydiving: Skydivers jump out of aircraft and parachute back to the ground, often for recreational purposes.