Increasingly complex mathematical systems were necessary to reconcile these new observations with of interlocking orbits. Nicholas Copernicus, a Polish astronomer, openly questioned the Ptolemaic system and proposed a heliocentric system in which the planets "including Earth orbited the sun This more mathematically satisfying way of the solar system di not attract many supporters at first, since the available data did not yet support a wholesale abandonment of Ptolemy's system. By the end of the 16th century, however astronomers like Johannes Kepler (1571-1630) had also begun to embrace Copernicus theory.