What is the Kármán line?

There is no sharp edge where the atmosphere ends; air simply gets thinner with height. The Kármán line, named after Hungarian-American engineer Theodore von Kármán, marks roughly the height at which the air is too thin for normal aircraft to fly using wings. The World Air Sports Federation (FAI) uses 100 km as the boundary for spaceflight records. The US military and NASA, however, award astronaut wings to people who fly above 50 miles, about 80 km. Satellites orbit much higher, usually from about 160 km upwards, because below that air drag would quickly pull them down.