Where does space begin?
What is Space?
Outer Space is the void between celestial bodies such as the sun, the moon, the earth and other bodies that are in the universe. Space is not empty though, but consists of a vacuum which is mostly a plasma of hydrogen and helium along with electromagnetic radiation, magnetic fields, neutrinos, dust and cosmic rays. The baseline temperature from the radiation created by the Big Bang now stands at around 2.7 Kelvins.
The National Aeronautics and Space Administration (commonly referred to as NASA) recognises an astronaut is someone who has flown at an altitude of 80,000 feet or higher, however the Karman line (which is where most say space starts) is 100,000 feet above sea level. Although the Karman Line is commonly viewed as the start of Space, it doesn't stand very firm even though it is considered by the FAI to be the start of space.
Because an astronaut only has to fly at an altitude of 80,000 feet some aircraft test pilots are considered astronauts even though they haven't crossed the Karman Line.