How can sky?

You would say "We went sky diving last Sunday" "Did you just hear that Susan went Sky Diving?" "James jumped out of the airplane without hesitation and it was the greatest example of sky diving...

The sky is the limit.Or,,The Sky's the limit.

It keeps you alive.....

That's a tough one. The sky, is basically the limit, as some people say. The sky though is actually the limit to our gravitational pull. Our atmosphere. (Wow I can't believe I spelled those two words...

Because otherwise we would be pulled into space.