How were Copernicus' and Kepler's theories about the movement of the planets similar How were they different?

Answer 1

Copernicus started the ball rolling with a new theory explaining how the planets move, using circles and epicycles as Ptolemy had done, but with the Sun assumed to be at the centre. He claimed that the new theory was simpler than Ptolemy's theory, which was later found to be not actually the case. But Copernicus's theory was used to predict the positions of the planets.

Later Tycho Brahe found ways of making accurate measurements of the planets' positions, and discovered small errors in predictions that were based on Copernicus's theory.

Kepler retained the idea that the Sun is at the centre, but used Tycho's measurements to research a new detailed theory of the planets' orbits. After long and arduous studies he discovered that the orbits are elliptical, and published three laws of planetary motion which were a huge step forward in scientific knowledge.

Newton made further discoveries that explained how elliptical orbits are produced by the Sun's gravity. He said he had stood on the shoulders of giants, and Kepler must have been at the front of his mind.

Kepler's achievement is enormous because the difference between an ellipse of the type that the planets move in and a circle with the Sun offset from the centre - as predicted by the old theory with epicycles - is extremely small.

Answer 2

They different because sun orbits