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Chatfield Senior High Physics
History of Astronomy
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Plato (4th C BC) Stars represent the heavens and are perfect
Sun, planets, and stars move in the “perfect” circle
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Aristarchus (3 C BC) First to propose the sun-centered universe (heliocentric) Not accepted because objects seemingly orbit around us
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Ptolemy (150 A.D.) Proposed the Earth-centered (geocentric model)
Must use circles for orbits, but must account for orbits as observed in the sky
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Retrograde Motion of Mars
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Ptolemaic Model (Geocentric)
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Copernicus ( ) Proposed the well accepted Sun-centered (heliocentric) model Not simpler than the earth centered due to circular orbits
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Copernican (heliocentric) Model
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Tycho Brahe ( ) Danish nobleman with a telescope set-up in his castle He observed planetary objects with great accuracy and over a long span of time
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Tycho Brahe’s Castle
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Tycho Brahe’s Stellar Map
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Johannes Kepler ( ) Used Tycho Brahe’s observation of Mars to develop a mathematical approach for orbital mechanics
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Kepler’s 1st Law A planetary orbit is an ellipse with the sun at one focal point
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Kepler’s 2nd Law Planets sweep out equal areas in equal times
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Kepler’s 3rd Law Periods and distance of orbits are related
T is period in years R is the average radius of orbit in astronomical units (AU) k is 1 for any planet orbiting the sun
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Applications of Kepler’s Laws
We will get to Mars through using the basic premises of these laws
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Galileo ( ) Galileo attacked the Catholic Church’s belief of a geocentric universe through scientific proof
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Dialogue of Two World Systems
This published document used satire to challenge the authority of the Catholic Church
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Moon craters Challenges perfection of heavens
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Galilean Moons of Jupiter
Moons orbit Jupiter instead of the Earth
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Galileo’s Finger!
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Isaac Newton ( ) In addition to the three laws of motion he developed the law of universal gravitation
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Law of Universal Gravitation
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Focus of Unit Kepler’s Laws of Motion as applied to Mars
Newton’s Law of Universal Gravitation Space exploration focusing on how spacecraft and eventually man will go to Mars
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