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22.1 Early Astronomy Ancient Greeks • Astronomy is the science that studies the universe • Deals with properties of objects in space & the laws under which the universe operates • Aristotle – Earth is round bc it always casts a curved shadow when it passes btw the sun & moon • Eratosthenes – established the size of Earth • Hipparchus – star catalog Geocentric Model • Earth was a sphere that stayed motionless at the center of the universe • The moon, sun, & the known planets – Mercury, Venus, Mars, & Jupiter – orbit Earth • Beyond the planets were hollow space, this is were the stars traveled daily around the Earth • Not a correct model Heliocentric Model • Sun centered model • Aristarchus was the 1st to believe this model • Earth & other planets orbit the sun • Although there was evidence for this model, the Earth centered model dominated Western thoughts for about 2000 yrs Ptolemaic System • Claudius Ptolemy • Presented a model of the universe • Accounted for the movements of the planets • Retrograde Motion results in a combination of the motion of Earth & the planet’s own motion around the sun The Birth of Modern Astronomy • Nicolaus Copernicus • Tycho Brahe • Johannes Kepler • Galileo Galillei • Sir Isaac Newton Nicolaus Copernicus • From Poland • Convinced that Earth is a planet just like the other five that were known • Daily motions of the heavens could be better explained by a rotating Earth • Changed the model of the solar system to having the sun at the center & the planets (Mercury, Venus, Earth, Mars, Jupiter, & Saturn) orbiting around it Tycho Brahe • Born 3 years after the death of Copernicus • Designed & built instruments called pointers which were used for 20 yrs to measure the locations of the heavenly bodies • Brahe’s observations, esp. of Mars, were far more precise than any that were previously made • Johannes Kepler was his assistant Johannes Kepler • Discovered 3 laws of planetary motion (pg. 618) • Discovered that the orbit of Mars around the sun was an oval shaped path = eclipse • Mars approaches the sun = speeds up • Mars moves away from the sun = slows down Galileo Galilei • Descriptions of the behavior of moving objects • Constructed his own telescope • Discovery of 4 satellites or moons orbiting Jupiter • Discovery that the planets are circular disks • Discovery that Venus has phases just like the moon • Discovery that the moon’s surface was not smooth • Discovery that the sun had sunspots, or dark regions Sir Isaac Newton • Was the 1st to formulate & test the law of universal gravitation • Inertia • Gravitational force decreases w/ distance • Greater the mass of the object, the greater its gravitational force REVIEW REVIEW REVIEW Location of Earth Location of Sun Supporters of Model Geocentric Model Center of Universe ________________ ________________ Heliocentric Model ________________ Center of Universe Aristarchus, Copernicus • What produces the retrograde motion of Mars? • What major change did Copernicus make in the Ptolemaic system? Why was this change so significant? • In your own words summarize Kepler’s 3 lays of planetary motion.