Yesterday, Austrian skydiver Felix Baumgartner (best known for jumping off skyscrapers) successfully completed a 39 kilometer dive from a balloon. Many media outlets described his jump as beginning “at the edge of space”, but the story is a little more complex than that.

One thing bothered me, though, about a lot of the coverage: many people said Baumgartner was jumping “from space” or “from the edge of space”. Don’t get me wrong—39 km is a long way up, about 4 times the altitude of commercial airliners, so I’m not denigrating this accomplishment at all. Atmospheric pressure is about 2% of its value at Earth’s surface at 39 km, and the temperatures are pretty cold, so Baumgartner had to wear a pressurized suit and carry an air supply. (If memory serves, the temperature was -7° C or 19° F when the dive began.) However, it’s not what is conventionally considered “space”: it’s within the region of Earth’s atmosphere known as the stratosphere (which also explains the project’s official name, “Stratos Jump”). So, if Baumgartner didn’t jump from space, where is the boundary of space? [Read more….]