Birth of Cosmological Models

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Birth of Cosmological Models
The History of Astronomy Chapters 4 5

• 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

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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

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Birth of Cosmological Models

• Greeks
• 427347 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

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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 Aristotles physics

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Birth of Cosmological Models

• Greeks
• A.D. 125 Ptolemy first astronomy textbook
• earth is spherical and at center of cosmos
  doesnt move
• predicted planetary motion in a GEOCENTRIC cosmos
  with accuracy
• accepted for 1,400 years

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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

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Copernicun Revolution

• 1507 started his writings
• Didnt 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

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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

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Galileo

• His evidence didnt 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

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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 Keplers third
  law

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Newton

• justified the Kepler-revised Copernican model
• accurately predicted the motions of the planets
• Impact of Newtons 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)