What is the difference between a celestial being and a celestial body? The first is something living such as an alien or an angel, whereas the latter is an inanimate object such as a star or a planet. Both, however, are from the sky.
The word celestial is primarily used to describe things that have to do with the heavens such as angels, spirits, stars and planets. It does not come from words meaning God or soul though, but from the Latin word for sky caelestis, which also gave rise to the word ceiling. So really, all you have to do is look up and you'll remember what celestial means — whether you're inside or outside.