Ptolemy: Consolidating Knowledge

Timelines of Events

• 150 CE
  • Ptolemy’s Almagest, Geography, and Tetrabiblos were written.
• 12th century BCE
  • The stars are arranged into constellations by the Babylonians.
• 350 BCE
  • Aristotle argues that the stars are fixed in place and Earth is unmoving.
• 135 BCE
  • Hipparchus generates a catalog of more than 850-star positions and brightnesses.
• 964 CE
  • Al-Sufi, a Persian astronomer, updates Ptolemy's star catalog.
• 1252
  • The Alfonsine Tables, which list the positions of the sun, moon, and planets based on Ptolemy's theories, are published in Toledo, Spain.
• 1543
  • Copernicus demonstrates that placing the sun at the center of the cosmos rather than Earth makes it far easier to predict the movement of the planets.

Ptolemy

• Ptolemy compiled all of the astronomical knowledge available at his time in Amalgest.

  • A thirteen-book mathematical treatment of the phenomena of astronomy. It covers a wide range of topics, including how the earth was created, the movement of the sun, moon, and stars, eclipses, and an explanation of how long a month is.

• The 17th-century star map makes use of Ptolemaic constellations.

  • The number of stars per constellation ranges from 2 to 42.

• In Ptolemy's depiction of the solar system, the heavens revolved around a stationary Earth at its center. To support his geocentric theory of the solar system, Ptolemy expanded and clarified Hipparchus' system of eccentric circles and epicycles.

• Everything that could be seen from a northern latitude of about 32° was listed in Ptolemy's catalog of 1,022-star positions and 48 constellations in the area of the celestial sphere known to the Greeks.

• To explain the motions of the Sun, Moon, and five planets at the time, Ptolemy's system required at least 80 epicycles.

• He believed the planets and sun orbited the Earth in the following order: Mercury, Venus, Sun, Mars, Jupiter, and Saturn.

• Mul Apin: A cuneiform tablet where the Babylonian constellations are listed.

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Early Quadrant

• Plinth: A massive rectangular stone block with one of its vertical sides perfectly aligned in the north-south plane.

  • The top of the stone had a horizontal bar, whose shadow accurately indicated the height of the sun at noon.

• He took daily measurements to determine the times of the solstices and equinoxes.

• He believed that the sun's orbit around Earth was circular.

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Ptolemy, the astrologist

• Ptolemy believed that the motions of the celestial bodies had a significant impact on what happened on Earth.
• Along with a method for calculating planetary positions, Ptolemy also produced a thorough analysis of how those movements affected people.

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