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The History of Astronomy

The History of Astronomy. Part Four Hipparchus and Ptolemy. Hipparchus (?-ca 127 BC). Made many advances including: Dividing the circle into 360 ° Created a Brightness scale called “Magnitude” Made a Catalog of Stars including: Name Location (on the Celestial sphere)

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The History of Astronomy

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  1. The History of Astronomy Part Four Hipparchus and Ptolemy

  2. Hipparchus (?-ca 127 BC) Made many advances including: • Dividing the circle into 360° • Created a Brightness scale called “Magnitude” • Made a Catalog of Stars including: • Name • Location (on the Celestial sphere) • Magnitude (His new brightness scale) Tried to get a Heliocentric Model to work…but found it required elliptical Orbits so he rejected it!

  3. Ptolemy (ca. 90-170) Claudius Ptolemaeus, or Ptolemy was an Astronomer, Geographer, and Mathematician whose works became the basis for Astronomy and Geography in Europe and the Muslim world for the next 1500 years He wrote the Almagest his model of the Universe. He had a Geocentric model with a spherical Earth, That rotates!

  4. The Problem of Retrograde Motion As a superior planet approaches opposition. It stops Moves backward awhile Then continue forward again. It’s called Retrograde Motion! The problem with a Geocentric Model is that it doesn’t explain this motion well

  5. The Ptolemaic System Ptolemy explained the retrograde motionof the planets by having them move in small circleswhich in turn move on larger circular orbits. These smaller circles called Epicycles! The epicycles make the planets move in loops around the Earth. Large loops forward (normal motion) and small ones back. (retrograde motion)! But still it wasn’t quite right

  6. Islamic Astronomy In Europe Ptolemy’s works were left unchanged. Islamic Astronomers were hard at work improving them. They made careful observations of the sky giving many stars the names that they still have today. They noticed that the Ptolemaic system was still a little off. So they added epicycles to the epicycles… …the system became insanely complex!

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