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Q. Where does Space begin? — Merl H.
A. It starts at an altitude of 100 kilometers.
People sometimes speak of 50 miles or 60 miles or 62 miles. The most widely accepted altitude where Space begins is 100 kilometers, which is about 62 miles.

The U.S. space agency awards astronaut status to persons who fly above 50 miles altitude.

For reference, note that a typical passenger jet cruises at an average altitude of about 30,000 feet which is just under six miles above Earth's surface. The most powerful military jets can't climb much above 100,000 feet, which would be just under 19 miles altitude.

The atmosphere gradually thins with increasing altitude so there is no tangible boundary between Earth's upper atmosphere and Space.

When people speak of "Outer Space," they refer to the vast region above Earth's atmosphere.


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