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270 BCE
Aristarchus of Samos
Aristarchus of Samos determined the Sun was about six to seven times larger than the Earth which led him to the idea of that the Earth actually revolves around the Sun. He concluded this by using spherical geometry and astrometry. -
150
Claudius Ptolemy
Claudius Ptolemy believed the Earth was the center of the universe. His model standardized geocentrism. For over a millennium, astronomers believed it was the right solar system model. Ptolemy's astronomy is based on the physics of Aristotle. -
1543
Nicolaus Copernicus
After years of observations (eyes) and calculations, Copernicus published 'On the Revolutions', just before his death. In it he proposed that the center of the universe was not the Earth, but the sun. He suggested that the Earth's rotation accounted for the rise and setting of the sun. He also proposed that Earth's motion caused the retrograde motion of the planets across the night sky (planets sometimes move in the same directions as stars, but sometimes they move in the opposite direction). -
Galileo Galilei
Galileo's observations of the phases of Venus proved Copernicus's heliocentric theory. He found that Venus goes through phases (like the moon), and this could't be possible if Venus revolved around the Earth. His assertion angered the church. Galileo’s telescope was modeled after telescopes in Europe that could magnify objects three times. His telescope could magnify objects up to twenty times. -
Johannes Kepler
Johannes Kepler created the first three laws of planetary motion "planets sweep out equal areas in equal times", "all planets move in ellipses, with the sun at one focus", and "the square of the periodic times are to each other as the cubes to mean distance". This laws helped him developed a heliocentric model in which all planets have elliptical orbits. He used his own geometric formulas for all his discoveries. -
Friedrich Bessel
Bessel was the first astronomer to publish the distance between stars and planets. He worked with this problem for 28 years, using the finest telescopes. He argued the stellar parallax (the sun only appears to move relative to more distant objects). His results provided the final proof of the heliocentric model of the solar system.
