In Classical times, there were two major
theories as to the existence of the Milky Way. The
Pythagoreans thought it was
residue left from the sun as it traveled that path (
Darn that slimy residue.)
Aristotle's
Peripatetics believed it was formed of
suspended exhalations. (
Darn that morning breath.) There was a third theory according to William Hone ( a nineteenth century author on the subject), proposed by
Democritus without the aid of a telescope. It was that the Milky Way contained innumerable fixed
stars which caused the white trail in the sky.
Of course,
Galileo gets all the credit. Just because he almost got tortured or something.