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The History of Astronomy ~ Chapters 4 & 5. Birth of Cosmological Models. Babylonians 1600 B.C.: first star catalogs compiled; recording of planetary motion 800 B.C.: planetary locations with respect to stars of zodiac 240 B.C.: observation of eclipses. Birth of Cosmological Models.

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birth of cosmological models

The History of Astronomy ~ Chapters 4 & 5

Birth of Cosmological Models
  • Babylonians
    • 1600 B.C.: first star catalogs compiled; recording of planetary motion
    • 800 B.C.: planetary locations with respect to stars of zodiac
    • 240 B.C.: observation of eclipses
birth of cosmological models2
Birth of Cosmological Models
  • Greeks ~600 B.C.
    • geometrical, physical models of cosmos – based on the ideal of the sphere as the perfect form
    • Pythagoras used geometry to develop a model of the cosmos
      • a series of concentric spheres centered around the earth – GEOCENTRIC
birth of cosmological models3
Birth of Cosmological Models
  • Greeks
    • 427–347 B.C. Plato – heavenly bodies move at a uniform rate
    • 384-322 B.C. Aristotle – used 56 spheres and took into account physical ideas of motion: natural motion & forced motion
birth of cosmological models4
Birth of Cosmological Models
  • Greeks
    • ~300 B.C.: Greek astronomer Aristarchus proposed a HELIOCENTRIC (sun-centered) model of cosmos
    • much of his writings were lost; model attacked because it contradicted Aristotle’s physics
birth of cosmological models5
Birth of Cosmological Models
  • Greeks
    • ~A.D. 125 Ptolemy – first astronomy textbook
      • earth is spherical and at center of cosmos & doesn’t move
      • predicted planetary motion in a GEOCENTRIC cosmos with accuracy
      • accepted for 1,400 years
copernicun revolution
Copernicun Revolution
  • Copernicus proposed a heliocentric universe
  • Marked the birth of modern science
  • Long association with the church
    • Reluctant to publish ideas that contradicted church teaching
copernicun revolution7
Copernicun Revolution
  • 1507 – started his writings
  • Didn’t authorized publishing until 1543 – he was dying
  • Hypothesis was correct – sun at center of cosmos
  • Model was inaccurate
    • His belief in uniform circular motion did not accurately explain the motion of the planets
galileo galilei
Galileo Galilei
  • Concentrated more on terrestrial physics than telescope observations
  • Used telescope to give support to Copernican model
  • Refuted two Aristotelian ideas:
    • Observations of moon geography dismissed the idea of a perfectly spherical body
    • Observations of Milky Way dismissed the idea of a set number of stars
  • Discovered four new “planets”
    • really the moons of Jupiter, therefore, things revolve around something other than the earth
galileo
Galileo
  • His evidence didn’t actually support the Copernican model, but it provided evidence against the Aristotelian-Ptolemaic model
  • Investigated and proposed “new” properties of physics: speed, velocity, acceleration, inertia, free-fall due to gravity
isaac newton
Isaac Newton
  • Provided laws of motion and gravity that apply on earth and in the celestial realm (goes against Aristotle)
  • Discovered:
    • laws of gravity that explain planetary motion.
    • that the force of gravity varies depending on the inverse square of the distance between two bodies.
    • The strength of the gravitation force depends directly on the product of the masses of the two objects and inversely on the square of the distance between their centers – this explains the elliptical orbits – supports Kepler’s third law
newton
Newton
  • justified the Kepler-revised Copernican model
  • accurately predicted the motions of the planets
  • Impact of Newton’s Laws: mathematical tool for:
    • placing satellites in orbit around earth
    • setting trajectories of spacecraft in solar system
    • defining the escape speed on an object from a planet (or the solar system itself)