Firmament, an ancient name for the vault of heaven. It is derived from the Vulgate or Latin translation of the Bible, in which the word firmavientum, denoting something solid and fixed, is used to translate the Hebrew term for the sky and stars. The latter expresses a different idea - that of extending by beating out. In ancient and medieeval times the sky was believed to be a solid revolving sphere of crystal, in which the stars were fixed, sharing its motion round the earth. When the difference in the planets' courses was observed, a new theory grew up, according to which there were several "crystalline spheres," each containing a certain number of fixed stars. The common notion was that there were nine, the nearest being that of the moon and the outermost the priinnm mobile, which set the others in motion. Heaven was somewhere beyond the primum mobile. This view of the universe - known as the "Ptolemaic system" - was upheld by the Church long after it had been dispelled by the discoveries of Copernicus and his followers. Any opinion which contradicted it was regarded as heretical, since it appeared incompatible with the statements of Scripture.