The sun

The sun was the stationary at the centre and that the earth and the planets moved in circular orbits around the sun.Nearly a centruy passed before this idea was takenseriously.Then two astronomers-the German,johannas kelper and the italian,Galileo Galiliei-started publicy to support the copernican theory despiter the fact that the orbits it predicted did now quite match the ones onserved .The death blow to the Atistrolien-ptolemaic theory came in 1609.In that year,Galileo started observing the night sky with a telescope which had just been invented.When he looked at the planet jupiter.Galileo found that it was accompinied by several small satellites or moons that orbited around it.This implied that every thing didnot have to orbit directly around the earth ,as Aristotle and ptolemy had thought.At the same time,johnanes leper had modified copernicus theory,suggesting that the planets moved not in circles but in ellipses.The preductions now finally matched the observations,but kelper could not reconcile them with his idea that the planets were made to orbit the sun by magnetic forces.An explanation was provided only much later,in 1687,when sir lsaac Newton published his philispher Naturalis principles Mathemaica in which he not only put forword a theory of how bodies move in space and time but aoso developed the complicated mathematics needed to analyyse thos motions .Newton postulated a law of universal graviation according to which each body in the universe was attracted toward every were to each other.It was this same force that caused objects to fall to the ground.Newton went on to show that according to his law,gravity the earth and the causes the earth and the planets to follow elliptical pathsaround the sun.