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 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.
- S. Sanz Fernández de Córdoba (2004-06-24). "The 100 km Boundary for Astronautics". Fédération Aéronautique Internationale. Retrieved 2014-05-07.
- O'Leary, Beth Laura (2009). Ann Garrison Darrin (eds.). Handbook of space engineering, archaeology, and heritage. Advances in engineering. CRC Press. p. 84. ISBN 1-4200-8431-3.CS1 maint: uses editors parameter (link)