Aristarchus(310-230 BC) Aristarchus was a Greek Astronomer and Mathematician. He proposed the heliocentric model of the Solar System. He attempted to measure the distances from the moon to the sun. Aristotle (334-322 BC) <span>Aristotle was a Greek Philosopher. He was the first person to propose this historical model. He thought the Earth was in the center of all celestial beings. His idea was that the Earth was in the middle of the sun, moon, stars, and other planets. </span> Ptolemy(100-170 CE) <span>Ptolemy was a astronomer and a geographer and a mathematician! He proposed the geocentric model. He believed that a celestial body could go at a constant speed in a perfect circle. It was called the "wheels-on-wheels" system. It had better observations than the model that had came before his. His geocentric model was used for the next 14 centuries! </span> Kepler(1571-1630) <span>German astronomer and mathematician, Johannes Kepler, studied very hard and closely, and he found out that the planets did not fit the observations that were made by previous explorers. He found one that fit the best out of them all! He found three principles, called Kepler's Laws. </span>
