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Questions • What was the first idea of how the universe was structured? • What is the correct idea of how the universe is structured? • Define: Heliocentric • Define: Geocentric • What is the Copernican Revolution? • Who was the first person to use the telescope to study space? Geocentric vs. Heliocentric A Battle for the Ages The Beginnings of the Geocentric Model of the Universe Early Greek Astronomy • Aristotle (384 – 322 BCE): States that the Universe is a perfect sphere with Earth at the Center. Objects in space also move in perfect circles. Early Greek Astronomy • Ptolomy: Still believed that Earth was center of Universe. Noticed that Aristotle’s model did not explain planetary movements. Ptolemy said that the planets and stars moved in EPICYCLES. In other words planets move in CIRCLES WITHIN CIRCLES! Ptolemaic System Mars Jupiter Ptolemy’s system provided the intellectual framework for all discussion of the universe for nearly 1600 years!! So in a very true sense, this idea was stupendously successful even though we now know that it was incorrect. Correction Added Saturn Earth & Moon •Epicycles added to epicycles •Precision Timing for Venus & Mercury •Earth placed “off” center. Mercury Sun Venus The Revolution of Ideas The Beginnings of the Heliocentric Model of the Universe Copernicus (1473-1543) “De Revolutionibus Orbium Coelestium” The Copernican Revolution! “On the Revolution of the Heavenly Spheres” 1. Earth is not the center of “everything.” 2. All the Planets revolve around the Sun! 3. Stars are very much farther away than the Sun 4. Any motion of the stars is a result of the Earth’s rotation 5. Any movement of the Sun is due to Earth’s rotation and revolution about the Sun. 6. Retrograde Motion was much easier to explain. Changing Ideas is Not Easy. Copernicus was no fool. He waited until his own death before he published his new ideas. On March 5, 1616, Copernicus' work was banned from being taught and discussed by the Congregation of the Index "until corrected." It stayed on this list of prohibited books and teachings until 1822!!!! Change is Hard. Copernicus still used “perfect” circles for the orbits. Copernicus ended up adding “epicycles!” At the time his theory was a complete disaster at “predicting” the positions of the planets in the sky. Ptolemy’s model “worked” much better. The PROOF! • Galileo Galilei: First to point the TELESCOPE towards the heavens. He studied the move and orbits of many nearby planets in our Solar System. Offered PROOF to Copernicus’s Heliocentric Model of our Universe. Galileo Galilei The Great Compromise Tycho Brahe (1546-1601) The Man with the Gold Nose Danish Nobelman Experimentalist & Observer. He actually made measurements Had his own observatory built. Made very careful measurements of star’s positions Tycho’s Observations Tycho’s Nova! – A “new” star appearing in the constellation Cassiopeia. Then dimished. (SN1572) Heavens can Change! A reason to doubt Aristotle! Maybe Ptolemy? Tycho’s Observations Made very precise measurements of stellar positions and planet positions in the sky Comet in 1577 is farther away than moon. Still “measured” no stellar parallax over an entire year. Earth must be stationary. Tychonic Model Tycho developed a system that combined the best of both worlds. He kept the Earth in the center of the universe, so that he could retain Aristotelian physics and Ptolemy’s geocentric idea. The Moon and Sun revolved about the Earth, and the shell of the fixed stars was centered on the Earth. But Mercury, Venus, Mars, Jupiter, and Saturn revolved about the Sun. Tychonic Model Tycho’s Contributions Lots of data! – Decades worth. He made the most precise observations that had yet been made by devising the best instruments available before the invention of the telescope. Decided by measurement and observation, NOT BY DOGMA His observations of planetary motion, particularly that of Mars, provided the crucial data for later astronomers The Student • Johannes Kepler: Followed Tycho’s work BUT followed the Heliocentric Model. Used Math to calculate that planets moved in ORBITS and along ELLIPSES. Kepler’s Laws of Planetary Motion Supported Newton’s Idea of Law of Universal Graviation Kepler’s Planetary Diagram Today! Questions • What was the first idea of how the universe was structured? • What is the correct idea of how the universe is structured? • Define: Heliocentric • Define: Geocentric • What is the Copernican Revolution? • Who was the first person to use the telescope?