 Because astronomical objects are at such remote distances, casual observation of the sky offers no information on their actual distances.All celestial objects seem equally far away, as if fixed onto the inside of a sphere with a large but unknown radius, 
which appears to rotate westward overhead; meanwhile, Earth underfoot seems to remain still.For purposes of spherical astronomy, which is concerned only with the directions to celestial objects, it makes no difference if this is actually the case or if it is Earth that is rotating while the celestial sphere is stationary.