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Greek Astronomy

Greek Astronomy. Ancient View of the Cosmos. Universe is 2-D All celestial objects attached to a sphere. Celestial Sphere is close Climb a high mountain and touch the sky Celestial objects are self-luminous Earth is the center of the universe Objects move on perfect circles.

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Greek Astronomy

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  1. Greek Astronomy

  2. Ancient View of the Cosmos • Universe is 2-D • All celestial objects attached to a sphere. • Celestial Sphere is close • Climb a high mountain and touch the sky • Celestial objects are self-luminous • Earth is the center of the universe • Objects move on perfectcircles

  3. Pre-disposition for success • Not Fatalists like Babylonians • Greeks had a curiosity about nature • Model builders

  4. Lunar Phases and Eclipses Two important changes in thought needed • Universe is three dimensional • Some celestial objects are dark

  5. Lunar Phases Phases

  6. 1st Quarter Full Moon New Moon

  7. Moon (3476 km) Earth (12,756 km)

  8. Lunar Eclipses Sun penumbra umbra Moon Earth

  9. Lunar Eclipses • Eclipse shadow is always a section of a circle • Earth must be a sphere • Color of the eclipsed moon

  10. Solar Eclipses

  11. Total Solar Eclipse

  12. North Pole Equator Alexandria 7° Sun’s Rays Syene Eratosthenes Video

  13. Eratosthenes • 7° is about 1/50th of a circle • Alexandria and Syene are separated by 800 km • That 800 km must be 1/50th the circumference of the Earth • Earth Circumference = 800*50 = 40,000 km • Accepted value is 40,074 km

  14. Relative sizes and distances • By 350 BC Greek Natural Philosophers knew the relative diameters and distances of the Sun, Moon, and Earth. • The Sun was very large and very far away and the Earth was bigger than the Moon.

  15. Cosmologies • Heliocentric Model • Aristarchus of Samos

  16. Cosmologies • Geocentric Model • Aristotle 350 BC

  17. Stationary Earth • Earth is heavy • Easier to imagine the sky can move • It looks like the sky is moving • We have no sensation of our motion • Rotating Earth would make objects fly off of the surface • StellarParallax

  18. June January Stellar Parallax • Hipparchus 150 BC Sun

  19. Why did Hipparchus fail to observe Stellar Parallax? • He only looked at bright stars. • He was a poor observer. • The stars are too far away. • The Earth does not orbit the Sun. 10

  20. Aristotelian UniverseTerrestrial Realm Earth and Water tend to sink • Composition predicts motion • natural tendencies Fire and Air tend to rise • Overall tendency to seek rest • Objects following tendencies require no force • Objects are corruptible (changing)

  21. Aristotelian UniverseCelestial Realm • Celestial Objects composed of Aether Self luminous but does not consume • Motion is constant,circular • Objects are incorruptible (not changing) Meteors and comets were phenomena of the Earth’s atmosphere

  22. Link

  23. Claudius Ptolemy (150 AD) • Accounted for retrograde motion within the confines of the Geocentric Model

  24. Earth Moon The Sun and Moon

  25. Deferent Epicycle Planet Earth The Planets Link

  26. Retrograde Loop inPtolemy’s System

  27. Ptolemaic Universe

  28. John Milton, Paradise Lost • With Centric and Eccentric scribl'd o're, Cycle and Epicycle, Orb in Orb

  29. Astronomy in the Dark Ages • Fall of Rome • Greek knowledge went to Islam • Alexandrian library destroyed • Universal Illiteracy • No mass communications • Villages were isolated • Thomas Aquinas • Giordano Bruno

  30. End of Section

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