Kepler defended and modified the Copernican view of the solar system with a radical reformation that established him as one of the great lights of the Scientific Revolution of the 16th-17th centuries. However, closed minds put Kepler's work at risk. In so doing, he calculated three laws involving the motions of planets that astronomers still use in calculations today. Using detailed measurements of the path of planets kept by Danish astronomer Tycho Brahe, Johannes Kepler (1571–1630) determined that planets traveled around the sun not in circles, as Copernicus had thought, but in ellipses. His ideas took almost a hundred years to gain credence, but Galileo's 1632 assertions that the Earth orbited the sun built upon the Polish astronomer's work, cementing the Copernican revolution. Copernicus published his book, De Revolutionibus Orbium Coelestium (' On the Revolutions of the Heavenly Spheres') when he was 70 and lay dying. The model wasn't completely correct, as astronomers of the time struggled with the backwards path Mars sometimes took, but it eventually changed the way many scientists viewed the solar system.Ĭopernicus, of Poland, felt the Ptolemaic view of the planets traveling in circular orbits around the Earth was over-complicated with many smaller circles, epicycles, needed to explain the intermittent retrograde motion of the planets (in which they appear to move in the opposite direction of the the stars).

In 16th century Poland, astronomer Nicolaus Copernicus (1473–1543) proposed a model of the solar system that involved the Earth revolving around the sun, according to NASA. Persian astronomer Abd al-Rahman al-Sufi (903–986), known as Azophi to Westerners, made the first known observation of a group of stars outside of the Milky Way, the Andromeda galaxy.

(Image credit: Bartolomeu Velho) Abd al-Rahman al-Sufi

The Ptolemaic geocentric model of the universe, devised by the Greek scientist Claudius Ptolemy, had everything revolving around Earth.

Eratosthenes flat earth