An example of an alternative conceptions once taken seriously by astronomers :
"The ancient Greek astronomer Eudoxus (about 408-355 B.C.[small caps]) introduced imaginary spheres into astronomical theory for the purposes of representing the apparent motions of the planets. These spheres were invisible, and the observable planet was regarded as situated, like a spot or point, on the surface of the invisible sphere. The planet was deemed to have no motion of its own, but simply to participate in the motion of the sphere to whose surface it was attached."
Rosen, E. (1959) Introduction to Three Copernican Treatises (Ed. E. Rosen) Dover Publications.
Although Eudoxus may have seen the set of spheres as an imaginary device, they were fro many centuries often taken as real (cystalline) spheres in which the heavenly bodies were embedded.
