lecture04 - Astronomy 3 The Nature of the Universe...

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Astronomy 3: The Nature of the Universe Professor Alice Shapley Lecture 4: Motion, Force, Energy (NGC 1499 Image credit: Markus Noller, Deep Sky Images)
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Logistics First homework quiz: due Monday, April 11 th , 10 pm.
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Logistics
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Logistics Lab this week on “Naked Eye Astronomy” (planetarium!). In case you are joining class this week, please contact Nassim Bozorgnia ( [email protected] ) about making up Week 1 lab.
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Review from Last Time Astronomy in the ancient world. Ancient Greek astronomy, geocentric model of the solar system, parallax. The Copernican Revolution and heliocentric model for the solar system. Copernicus, Tycho, Kepler, Galileo. Kepler’s laws. The role of Galileo.
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Like the Sun, planets usually appear to move eastward relative to the stars over many weeks. But, sometimes, they move west relative to the stars for a few weeks or months. This is called retrograde motion. Noticeable only over many nights; on a single night, a planet rises in east and sets in west… The name planet is based on the Greek word for “wanderer.”
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The apparent angular shift of a star’s position as Earth orbits the Sun. The nearest stars are much farther away than the Greeks thought. The parallax angles of the stars are so small, that you need a telescope to see them. A telescope provides much more magnification than the human eye. Telescopes were not invented until the 1600s.
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Each planet, and the Sun, is assumed to orbit around an empty point in space which itself circles around Earth. (Think of Spirograph) Animation: http://www.astro.utoronto.ca/ ~zhu/ast210/geocentric.html
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Kepler’s three laws: 1. The orbit of each planet is an ellipse with the Sun at one focus. 2. As a planet moves around its orbit it sweeps our equal areas in equal times. 3. More distant planets orbit the Sun at slower average speeds: p 2 = a 3 . Kepler’s second law How did Copernicus, Tycho and Kepler challenge the Earth-centered idea? Copernicus created a sun-centered (heliocentric) model; Tycho provided the quantitative data needed to improve this model; Kepler found a model that fit Tycho’s data.
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How can we distinguish science from nonscience? Great example of the scientific method:
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Modern science seeks explanations for observed phenomena that rely solely on natural causes.
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Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. (Simplicity = “Occam’s razor”) Based on a 14 th century English friar named William of Ockham; Occam’s razor is a statement that, all things being equal, the simplest explanation tends to be the right one. It is a guiding principle.
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A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations.
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Based on proposing and testing hypotheses.
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