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400
Aristotle's Theory
Aristotle held that all earthly matter were made of the elements: air, water, earth, and fire. -
500
Leucippus and Democritus
In the 5th century B.C.E Leucippus and Democritus proposed that all matteris composed of tiny, indivisible particles. -
Jan 1, 1514
Copernicus and his Theory
Nicalaus Copernicus made a handwritten book called "On the Revolution of the Celestial Spheres." Copernicus believed that the earth and all other planets in our solar system rotate around the sun, inspite of the beliefs that everthing orbited around the Earth. -
Galileo is summoned
Galilieo Galilei was an Italian astronomer, and he believed in Copernicus' theory, despite the belief that Aristotle's theory was true. Galileo was summoned to Rome and warned not to teach or write on the contriversial theory. -
Galilieo is arrested
Galileo published work on the Copernicun system. He was found guilty of heresy, and was placed under house arrest for the last nine years of his life. -
Period: to
Pluto i
Pluto was considered to be a planet until things changed! -
Pluto is Discovered
When pluto was discover, it was significantly larger than any known to be near it in the solar system. So, at the time, it made sense to consider it a planet. -
Astronomers make a new discovery
With the benefit of better technology, astronomers discovered the Kuiper Belt [ky-per-belt], an area of rocks, asteroids, and other space debris located just beyond Neptune. -
Quoar
A body named Quoar was discovered and was about half as large as Pluto. -
Sedna
A body named Sedna was discoverd and was only a few hundred kilometers smaller than Pluto. -
Eris
Finally, in 2005, Eris, which was larger than Pluto, was also discovered. -
Pluto is NOT considered a planet anymore
The controversy came to a head in 2006, when the International Astronomical Union voted to create a new category of planets called dwarf planets. They put Pluto into it, along with Eris and Ceres, the largest body in the asteroid belt.