Where does space begin?
There is no sharp boundary, but space is commonly said to begin at the Kármán line, 100 kilometers above sea level. The US military and NASA often use 80 kilometers (50 miles) instead.
Earth's atmosphere gets thinner with height and slowly fades into space. About 99 percent of the air lies below about 30 kilometers. Because there is no clear edge, scientists and organizations have chosen different boundaries for practical purposes, such as deciding who counts as an astronaut.
The Fédération Aéronautique Internationale, which keeps records for aviation and spaceflight, uses 100 kilometers. The US Air Force, the Federal Aviation Administration and NASA award astronaut wings to people who fly above 50 miles, about 80 kilometers. Some scientists argue that 80 kilometers is a better physical boundary.
Higher than you think
Commercial airliners fly at about 10 to 12 kilometers. Weather balloons can reach about 35 kilometers. The International Space Station orbits at about 400 kilometers, and GPS satellites at about 20,000 kilometers.
Did You Know?
Short suborbital flights by companies like Blue Origin cross the 100-kilometer line and give passengers a few minutes of weightlessness.