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Period: 700 BCE to 100
Ancient Greek Astronomers
Using only their eyes, ancient Greek observers were able to identify the five visible planets - Mercury, Venus, Mars, Jupiter, and Saturn. While not understanding that they were bodies orbiting the Sun, they knew that they were different that the other stars in the sky. The word planet comes from the ancient Greek for "wandering star." -
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Ptolemy
Greek scientist who described the geocentric model of the solar system: the Sun, Moon, planets, and the stars all orbit around the Earth in perfect circles -
Apr 8, 1543
Nicolaus Copernicus
Polish scientist who described the heliocentric model of the solar system: Earth, the planets, and the stars orbit the Sun. The Moon still orbits the Earth -
Tycho Brahe
Danish astronomer who took daily detailed measurements of the position of the planets for over twenty years. He did not use a telescope and improved the equipment used for measuring stellar planets. -
Johannes Kepler
German astronomer who worked for Brahe and used his measurements to calculate that planetary orbits were elliptical (AKA ovals) and not perfect circles as previously thought. -
Galileo Galilei
Italian scientist who disproved the geocentric model by using a telescope to demonstrate that Jupiter had its own moons. By proving that the moons moved around Jupiter and not Earth, it made it clear that the geocentric model, where everything orbits the Earth, was incorrect. -
Sir Isaac Newton
British mathematician and scientist who developed the theory of universal gravitation, which explained why the planets orbited the Sun in elliptical orbits, confirming Kepler's work -
Anders Johan Lexell
Finnish Swedish who calculated Uranus’ orbit using Newton's Law of Universal Gravitation, proving that it was a newly discovered planet. Uranus was first reported be a comet by Sir William Herschel in 1781. -
Urbain Le Verrier
French astronomer who used Newton's Theory of Universal Gravitation to predict the location of new planet beyond the orbit of Uranus. The planet Neptune was discovered where he predicted by observers at the New Berlin Observatory in Germany. -
Clyde Tombaugh
American astronomer who discovered Pluto and its moon Charon. He used predictions from Percival Lowell and William Pickering to search the sky and locate what was being called "Planet X" at the time.
