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Cool Dudes of Astronomy! a.k.a A brief history of astronomy Ancient Greeks • Observed patterns in the stars that didn’t move or change- the stars moved, but stayed in the same position relative to each other. • Observed 5 points of light that seemed to wander among the stars – planets (wandering star) • Mercury • Venus • Mars • Jupiter • Saturn Earth was the center of the universe geocentric Greek for Earth center http://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html Ptolemy Curt Suplee, Milestones of Science p.24 • AD 140 • Greek Astronomer • Earth is the center of a system of planets • The planets move on little circles that move on bigger circles around the earth http://www.polaris.iastate.edu/EveningStar/Unit2/unit2_sub1.htm • This vision of the Ptolemaic universe from a 1660 celestial atlas, shows the position of the Earth surrounded by the celestial circles • These ideas lasted for 1400 years! Curt Suplee, Milestones of Science p.24-25 Copernicus • Believed the sun was at the center of the universe • Heliocentric Sun • His work was published in1543 – while he was on his deathbed! Galileo • ~100 yr after Copernicus • Observed 4 moons revolving around Jupiter • Observed Venus has phases like our moon Galileo cont. Neither of these observations can be explained with Earth at the center, therefore the sun is at the center! Copernicus was correct!! Galileo believed the orbits are circles Tycho Brahe (TEE koh BRAH uh) 1546-1601 • Danish Astronomer – made very careful observations of the planets for almost 20 yr. Johannes Kepler 1600’s • Analyzed Brahe’s data • Discovered the orbit of each planet is an ellipse. Sir Isaac Newton • Inertia and gravity combine to keep the planets in orbit!