How far is the sky?
That depends on the definition of sky. Is it the air above you?
Then it is quite close. Three quarters of the air is within 11 km
of the surface but space craft notice the beginning of atmosphere
as far out as 120 km. Somebody has to make a decision on where the
Earth's atmosphere finishes and space begins - they did. The Karman
line at 100 km is the "official" beginning of space. Where would
you have difficulty breathing? At around two kilometres or