They are the same, except 'over' has one situation where it can be used but 'above' can't. 'over' can be used like the verb 'cover' to describe something touching another thing. For example: The blanket is over the back of the couch. You can't use 'above' here. The hole was covered over with dirt. There are mosquitoes all over the place! 'all over the place' is a common expression. When I think of the sky, I think of it 'covering' the whole world, so 'over' is okay. The sky is also 'above' us, meaning we see it if we look straight up. Prepositions are confusing. I'm sure my explanation doesn't cover everything, but I hope it helps.