The Karman Line

The Kármán line lies at an altitude of 100 km (62.1 miles) above the Earth's sea level, and is commonly used to define the boundary between the Earth's atmosphere and outer space. The line was named after Theodore von Kármán, a Hungarian-American engineer and physicist who was active primarily in the fields of aeronautics and astronautics. He first calculated that around this altitude the Earth's atmosphere becomes too thin for aeronautical purposes