Does the sun revolve around the earth? Does the earth revolve around the sun? Is the sun the centre of the universe? Such questions taxed the minds of early scientists and non-scientists alike. In 1609 Johannes Kepler formulated the first two of his three planetary laws of motion which provided answers to thiese questions. The first law states: the planets (including the earth) move about the sun in elliptical orbits with the sun at one focus. Kepler discovered his laws by sifting through a great mass of astronomical data obtained from observations of the planets by Tycho Brahe who had died in 1601. Kepler’s discoveries were all the more amazing because the calculus had not then been discovered.
