Day 70

Have you ever wondered about how high up it is to space - like as in where the blue sky ends and the black space stuff starts?  My kids did the other day and we had a range of guesses from "hmm, I'm pretty sure it's like about 2 km's" (mine) to "it's about a gazillion" (Smith's) - which got me thinking that I had to find this out.


How High is the Earth's Atmosphere?



The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention and reducing temperature extremes between day and night. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. An altitude of 120 km is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Kármán line, at 100 km also is often regarded as the boundary between atmosphere and outer space.  On average, however, a good number to use for the true height of the atmosphere is about 122km. It is at this altitude that vehicles such as the Space Shuttle are said to make "atmospheric interface" when they re-enter the atmosphere prior to landing. Another "official" value you might consider is 80.5km. Anyone flying higher than this altitude is officially considered an astronaut by NASA and the US Air Force.  Just for comparison, controlled airspace, which is the portion of the atmosphere regulated by government agencies (ie where normal planes fly)  is only 18kms.
2km?  What was I thinking?  I think Smith was a little closer than me.

Interesting huh!