Galileo, Brahe, and Kepler

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Galileo, Brahe, and Kepler
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Galileos Experiments (1564-1642)

• Galileo tried something new doing experiments!
• Dropping balls to measure gravity
• Rolling balls to examine inertia
• Observing the sky through a telescope

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What Galileo Saw

• An imperfect Sun (sunspots)

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What Galileo Saw

• An imperfect Sun (sunspots)
• A Moon with mountains and craters

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What Galileo Saw

• An imperfect Sun (sunspots)
• A Moon with mountains and craters
• The ears of Saturn

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What Galileo Saw

• An imperfect Sun (sunspots)
• A Moon with mountains and craters
• The ears of Saturn
• Four moons orbiting Jupiter

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What Galileo Saw

• An imperfect Sun (sunspots)
• A Moon with mountains and craters
• The ears of Saturn
• Four moons orbiting Jupiter
• The phases of Venus

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Tycho Brahe Measurements

• Tycho Brahe (without a telescope) made extremely
  accurate measurements of the positions of the
  stars and planets over the course of 20 years.

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Tycho Brahes Model

• Earth at the center of the Universe (because
  parallax is not seen)
• The Sun travels about the Earth in a perfect
  circle
• The planets move around the Sun in perfect circles

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Keplers Analysis

• By working for Tycho Brahe (and then stealing the
  data after Tychos death), Johannes Kepler had
  access to the most precise data on planetary
  positions in history.
• He fit the data in every way imaginable.

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Keplers Laws
First define the distance from the earth to the
Sun to be 1 Astronomical Unit (1 A.U.)

• Keplers Laws
• Planets move in ellipses with the Sun at one focus

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Keplers Laws
First define the distance from the earth to the
Sun to be 1 Astronomical Unit (1 A.U.)

• Keplers Laws
• Planets move in ellipses with the Sun at one
  focus
• Planets in their orbits sweep out equal areas in
  equal times

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Keplers Laws
First define the distance from the earth to the
Sun to be 1 Astronomical Unit (1 A.U.)

• Keplers Laws
• Planets move in ellipses with the Sun at one
  focus
• Planets in their orbits sweep out equal areas in
  equal times

• The period, P, of an orbit (in years) squared is
  equal to a, the semi-major axis of the orbit (in
  A.U.) cubed. In terms of mathematics, P2 a3

These laws are empirical Kepler knew no reason
for them
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Keplers Laws
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Summary

• Galileo Father of experimental science
• Tests of inertia and acceleration
• Observed the sky with a telescope heavens not
  perfect
• Tycho Brahe
• Recorded very precise positions of the planets
  with naked eye
• Wanted Kepler to fit his data with a modified
  geocentric model
• Kepler
• Discovered 3 mathematical laws that could fully
  describe the motions of the planets (but without
  any physical basis)