As regards him coming from the heavens: I believe this will be a spectacular event that everyone would recognise as a miracle and that nobody will miss. Personally, I imagine clouds parting, rays of sunshine, angels, all that sort of thing
Who is everyone, when we look up into the sky in Texas, we do not see the same sky that Oklahoma does, or even the next city over who may have hale falling from the sky when we have a clear blue sky. The skies are different all over the world Which part of the sky in what part of the world will be able to see him?
We may not be able to see him in the sky. There is no such thing as the world looking up being able to see him.
When the bible was written, they were in Jeruslem and or Greece or around the same area, they must have been talking to that one part of the world. There's no scientific way for all people to look up into the skies and see the same thing, no such thing .
But then again the bible also says that Jesus said that generation would not fade away before he came back so, he must have been speaking to that crowd, that generation.