Outer space

Outer space (also called just space) as a name for a region, refers to the relatively empty parts of the Universe, outside the atmospheres of celestial bodies. The term outer space is used to distinguish it from airspace and terrestrial locations. Although outer space is certainly spacious, it is now known to be far from empty, and filled with a tenuous plasma.

Milestones on the way to space

• Sea level - 1 bar of atmospheric pressure
• 4.6 km (15,000 ft) - FAA requires supplemental oxygen for aircraft pilots and passengers
• 5.0 km (16,000 ft) - 0.5 bar of atmospheric pressure
• 5.3 km (17,400 ft) - Half of the Earth's atmosphere is below this altitude
• 8.8 km (29,035 ft) - Summit of Mount Everest, the highest mountain on Earth
• 16 km (52,500 ft) - Pressurized cabin or pressure suit required
• 18 km (59,000 ft) - Boundary between troposphere and stratosphere
• 20 km (65,600 ft) - Water at room temperature boils without a pressurized container (the popular notion that bodily fluids would start to boil at this point is false because the confines of the body generate enough pressure to prevent actual boiling)
• 24 km (78,700 ft) - Regular aircraft pressurization systems no longer function
• 24.7 km - Altitude record for manned balloon flight
• 32 km (105,000 ft) - Turbojets no longer function
• 45 km (148,000 ft) - Ramjets no longer function
• 50 km (164,000 ft) - Boundary between stratosphere and mesosphere
• 80 km (262,000 ft) - Boundary between mesosphere and thermosphere
• 100 km (328,084 ft) - Kármán line, defining the limit of outer space according to the Fédération Aéronautique Internationale. Aerodynamic surfaces no longer function due to lack of atmospheric pressure
• 120 km (400,000 ft) - First noticeable atmospheric effects during reentry from orbit
• 200 km - Lowest possible orbit with short-term stability (stable for a few days)
• 350 km - Lowest possible orbit with long-term stability (stable for many years)
• 690 km - Boundary between thermosphere and exosphere