Kármán line

The boundaries between the Earth's surface and outer space, at the Kármán line, 100 km (62 miles) and exosphere at 690 km (430 miles). Not to scale.

The Kármán line is the altitude where space begins. It is 100 km (about 62 miles) high. It commonly represents the border between the Earth's atmosphere and outer space. This definition is accepted by the Fédération Aéronautique Internationale (FAI). The FAI is an international standard setting and record-keeping body for aeronautics and astronautics. The line is named after Theodore von Kármán (1881–1963), a Hungarian-American engineer and physicist. He was active in aeronautics and astronautics. He was the first to calculate that around this altitude, the atmosphere becomes too thin to support aeronautical flight. An aircraft at this altitude would have to travel faster than orbital velocity (velocity at which a body moves around another body.) to obtain enough lift to support itself. There is a sudden increase in temperature of the atmosphere and solar radiation just below the line. This places the line within the greater thermosphere.