1. Geocentric vs. Heliocentric A Battle for the Ages

2. Jupiter Saturn Mars Venus Earth & Moon Mercury Sun 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. Ptolemaic System Correction Added Epicycles added to epicycles Precision Timing for Venus & Mercury Earth placed “off” center.

5. Earth Equant Epicycle Deferent The planet moves along its epicycle as the epicycle moves along the deferent around the Earth. To make the observations as accurate as possible, it was necessary to place the Earth slightly off center of the orbits, but to preserve symmetry that meant that there was an equal place (“Equant”) opposite the Earth from the center. The combined motion of the planet and the resulting retrograde motion are shown. Off Center?!

7. The Revolution of Ideas The Beginnings of the Heliocentric Model of the Universe

8. Copernicus (1473-1543) “De Revolutionibus Orbium Coelestium”

9. “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.

10. Earth 1 Sun 1 2 3 4 5 6 6 Outer Planet 5 4 3 2 Fixed Stars Planet's apparent path around sky. Earth overtakes slow outer planet so the outer planet appears to slow down, move in reverse, and then move forward again with respect to the fixed stars. Retrograde Motion

11. Changing Ideas is Not Easy. 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!!!! Copernicus was no fool. He waited until his own death before he published his new ideas.

12. 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.

13. The Great Compromise Tycho Brahe (1546-1601)

14. 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

16. 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?

17. Tycho’s Observations Made very precise measurements of stellar positions and planet positions in the sky Still “measured” no stellar parallax over an entire year. Earth must be stationary. Comet in 1577 is farther away than moon.

18. 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.

19. Tychonic Model

20. 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

21. Tycho No More History or Myth? How did Tycho die?