Is the World Government aware of the existence of the Sky Island? Sky Island is a myth or a legend to many people including the pirates form Jaya, who laugh at Luffy because he thinks that Sky Island exists.  

Does the World Government know about Sky Island or is it just a myth to them?
I believe that the world government does not know of the Sky Islands, because when the Straw Hats land in Navarone, the officials do not believe Zoro, Luffy, or any of them when they say they came from the sky.  Considering Navarone was a huge Marine Base, if the World government knew of the Sky Island, they would have let them know.