In
Europe at the time when the
Greek astronomer Ptolemy's (ad 127-151) view of the
cosmos as a
universe of
interlocking spheres became the
orthodoxy, there was a widely accepted and very
poetic explanation for 'falling stars' which was entirely
consistent with other deeply held
beliefs of the time.
It was thought that the gods, overwhelmed with curiosity, would sometimes look at the earth from between the spheres, and that in that instant a star or two might slip through the gap and become visible as a falling or shooting star. Since the gods were clearly peering down at that very moment, it was considered an excellent opportunity to voice one's wishes with the guarantee that the gods would hear them.
This is probably where the idea of wishing on a falling or shooting star comes from, although I note that, "similar superstitions are widespread even in cultures remote from Europe: in Chile, you must pick up a stone in the same moment, and in the Philippines tie a knot in a handkerchief" (1)
Sources:
- (1) 'Cosmic Debris' by Mike Jay in Fortean Times magazine (FT 143) is well written and broad in scope, raising many interesting points regarding the mutable nature of accepted belief. I strongly recommended it.
I had heard this explaination before somewhere, but had forgotten all about it until the article referenced above brought it back to me and filled out the details.