This is very interesting. I still suffer from fear of looking at the sky slightly since I developed existential terror. I became aware of mortality and existance and the "size" and scale of everything. It was horrible at the time.
What helped most was to become aware of the fact it wasn't the sky I was afraid of, it was the fear of my mind not being able to cope with the idea of the sky, that scared me. Does that make sense? Most fears relate to your mental handling of the problem, not the problem itself, which is why they grow. You need to teach yourself you won't go mad or blow up if you look at the sky through gradual exposure. It's hard as it's there all the time to remind you, but it can be done. Good luck!