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Astro 102/104
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Lecture #3: Orbits and Gravity
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Laws of Planetary Motion:
– Kepler's Laws.
– Newton's Laws.
• Gravity.
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Planetary Orbits.
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Spacecraft Orbits.
Astro 102/104
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The Main Point
Motions of planets, moons, and
asteroids can be very accurately
predicted because of the underlying
laws of planetary motion and gravity
discovered by Kepler and Newton.
Astro 102/104
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Laws of Planetary Motion
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Ptolemaic (geocentric) and Copernican
(heliocentric) systems made specific predictions
about where the planets would be over time.
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What was needed was high quality
data
to test
these competing models.
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Tycho Brahe (1546-1601):
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20+ years of careful measurements.
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Best data available, and pre-telescopic!
Astro 102/104
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The Scientific Method
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