High (8,000 - 12,000 feet [2,438 - 3,658 meters]), Very High (12,000 - 18,000 feet [3,658 - 5,487 meters]), and Extremely High (18,000+ feet [5,500+ meters]).
The death zone is the name used by mountain climbers for high altitude where there is not enough oxygen for humans to breathe. This is usually above 26,247 feet (8,000 metres).
8,000 feet = 1.5 miles
10,000 feet = 1.89 miles
15,000 feet = 2.84 miles
20,000 feet = 3.79 miles
25,000 feet = 4.74 miles
Average altitude of a plane:
Most commercial jetliners cruise somewhere between 30,000 and 45,000 feet above mean sea level.
Mars and Nasa
Click links below to find answers from NASA:
Other items of interest:
Videos of potential interest:
The Unbearable Beauty of the Night Sky (video 7 min)
NOvA: Exploring Neutrino Mysteries (Video: 5:52 min)
Other items of potential interest:
Can you hear sounds in space? (Cornell University)
New Data to Put Cosmic Light Speed Limit to the Test (NPR 4 min audio)