The Depth of the Heavens – Belief and Knowledge During 2500 Years

Abstract

For Dante Alighieri (1265-1321) the spiritual cosmos contained the Heavens, Earth and Hell, and it was compatible with the physical cosmos known from Aristotle (384-322 B.C.). Dante’s many references in his Divine Comedy to physical and astronomical subjects show that he wanted to treat these issues absolutely correctly. Tycho Brahe proves three hundred years later by his observations of the Stella Nova in 1572 and of comets that the spheres of heavens did not really exist. It has ever since become more and more difficult to reconcile the ancient ideas of a unified cosmos with the increasing knowledge about the physical universe. Ptolemaios derived a radius of 20 000 Earth radii for the sphere of fixed stars. This radius of the visible cosmos at that time happens to be nearly equal to the true distance of the Sun, or 14 micro-light-years. Today the radius of the visible universe is a million billion (1015) times larger than Tycho Brahe believed. The lecture gave an overview of astronomical distances and their dramatic change during two and a half millennia, the following text is an extract hereof.

Keywords

• history and philosophy of astronomy
• astrometry
• cosmology
• distance scale