1. Announcements Exam 1 results: most scored in the 80’s with one 91 and two lower than 70. Dark Sky Observing Night tonight is cancelled. Hope for clear skies next Tuesday

2. Presentations on the Origin Myth of a culture

3. Aristarchus: ahead of his time 310 – 230 BCE Most of his writings are lost Measured the Earth-Moon distance (not too far off) and the Earth-Sun distance (way off) along with the relative sizes of the Moon and Sun. Found that the Sun is much larger than the Earth so he proposed the Earth went around the sun

4. Hipparchus 190 – 120 BCE Proposed a geocentric model with an epicycle and eccentric. The distance from Earth to the center was called the eccentric.

5. Claudius Ptolemy: an Alexandrian 87 – 150 AD Put finishing touches on geocentric model of the heavens Complete mathematical model for calculating planetary positions at any time into the future (almost) Wrote an extensive text on astronomy, astrology and mathematics now called the Almagest

6. Ptolemy placed the Earth at the center (almost) The Equant was equidistant from the center of the deferent and on the opposite side of the center from the Earth. center

7. With Ptolemy’s system, the retrograde motion of a planet could be explained

8. The Ptolemaic Model of the Universe Each planet had its own eccentric so the center of the deferent was different for each planet. The size of the deferent, the size of the epicycle and the speed of the planet on each could be adjusted to match the observed motion of the planet fairly closely. Watch Museo Galileo Epicyclic Motion video

9. Using geometry and recent observations, planetary positions could be recalculated

10. Nicholas Copernicus 1473 – 1543 The Sun is the center Mathematical model no better than Ptolemy’s Model had predictive power Watch video from Museo Galileo on the Copernican System