How far is Earth from space?

NASA considers people to be astronauts once they've traveled higher than 80 km (50 miles). The earth's atmosphere officially ends at approximately 800 km (500 miles) but shuttles and the northern lights have been seen at altitudes of around 690 km (431 miles).
Various agencies have designated lower altitudes for the beginning of space. The Federation Aeronautique Internationale has established the Karman line at an altitude of 100 km (62 miles).
The reality is that there is no clear boundary between the Earth and outer space.
I am not no NASA but I would say around 20Miles up from Ground we would be in Space, it kind of hard to believe but if you think a plane climbs around 1mile, -50 degrees, and you travel up another 19 miles you would be in no gravity Zone with no air, so to me that's the point of Space.
If I am wrong then I can live with that, but it would be good to get exact zone and degrees.
As for shuttles and northern lights, well they are both seen at low altitudes, however you can see satellites very clearly from you own back garden on clear night. So space and orbit can not be that far as its only approx 250klm above ground level which you can see the Space station very clear.