The Big Four:

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The Big Four

• Copernicus
• Planets orbit Sun, not Earth
• but assume circular orbits (Greek idea of
  perfection)
• Kepler
• Orbits elliptical, not circular
• but described by simple laws
• Galileo
• Discovers moons of Jupiter
• Orbital motion is Universal
• Newton
• Idea of forces theory of gravity

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Newtons Theory Idea of Escape Velocity

• Gravity is a force
• causes acceleration or deceleration ( negative
  acceleration)
• g at Earths surface 32 ft/sec/sec 22
  mph/sec 9.8 meters/sec/sec
• Example
• throw something up at 66 mph it stops after 3
  sec, then falls back in another 3 sec
• How to calculate gravitational pull of a mass
• increases with amount of mass
• decreases with square of distance from center of
  mass

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Escape speed
Competition deceleration vs. weakening of
gravity with distance
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The Speed of Light

• 1675 Olaus Roemer (Danish astronomer) measures
  by timing transits of Jupiters moons

Kaufmann, Universe, 4th ed., p.80
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The Idea of a Black Hole

• John Michell (1783) , Pierre-Simon Laplace
  (1796)
• Ques What happens if the escape speed from an
  object is greater than the speed of light?
• Ans If light consists of particles of matter,
  they would not be able to escape
• The catch early 19th cent - light is a wave (a
  disturbance), not a particle
  BH idea forgotten.

dark star ?
until Einstein comes along