<Tr> <Td> </Td> <Td> The examples and perspective in this article may not include all significant viewpoints . Please improve the article or discuss the issue . (June 2015) (Learn how and when to remove this template message) </Td> </Tr> <P> Not all Greeks agreed with the geocentric model . The Pythagorean system has already been mentioned; some Pythagoreans believed the Earth to be one of several planets going around a central fire . Hicetas and Ecphantus, two Pythagoreans of the 5th century BC, and Heraclides Ponticus in the 4th century BC, believed that the Earth rotated on its axis but remained at the center of the universe . Such a system still qualifies as geocentric . It was revived in the Middle Ages by Jean Buridan . Heraclides Ponticus was once thought to have proposed that both Venus and Mercury went around the Sun rather than the Earth, but this is no longer accepted . Martianus Capella definitely put Mercury and Venus in orbit around the Sun . Aristarchus of Samos was the most radical . He wrote a work, which has not survived, on heliocentrism, saying that the Sun was at the center of the universe, while the Earth and other planets revolved around it . His theory was not popular, and he had one named follower, Seleucus of Seleucia . </P> <P> In 1543, the geocentric system met its first serious challenge with the publication of Copernicus' De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres), which posited that the Earth and the other planets instead revolved around the Sun . The geocentric system was still held for many years afterwards, as at the time the Copernican system did not offer better predictions than the geocentric system, and it posed problems for both natural philosophy and scripture . The Copernican system was no more accurate than Ptolemy's system, because it still used circular orbits . This was not altered until Johannes Kepler postulated that they were elliptical (Kepler's first law of planetary motion). </P> <P> With the invention of the telescope in 1609, observations made by Galileo Galilei (such as that Jupiter has moons) called into question some of the tenets of geocentrism but did not seriously threaten it . Because he observed dark "spots" on the moon, craters, he remarked that the moon was not a perfect celestial body as had been previously conceived . This was the first time someone could see imperfections on a celestial body that was supposed to be composed of perfect aether . As such, because the moon's imperfections could now be related to those seen on Earth, one could argue that neither was unique: rather, they were both just celestial bodies made from Earth - like material . Galileo could also see the moons of Jupiter, which he dedicated to Cosimo II de' Medici, and stated that they orbited around Jupiter, not Earth . This was a significant claim as it would mean not only that not everything revolved around Earth as stated in the Ptolemaic model, but also showed a secondary celestial body could orbit a moving celestial body, strengthening the heliocentric argument that a moving Earth could retain the Moon . Galileo's observations were verified by other astronomers of the time period who quickly adopted use of the telescope, including Christoph Scheiner, Johannes Kepler, and Giovan Paulo Lembo . </P>

The first scientist to question the geocentric model was