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Lecture 20 - • Modern views of solar system • Solar...

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1. Andromeda Galaxy in on a collision course with our own 2. What are spiral nebulae? o Didn't know they were galaxies at the time o Two camps for Great Debate Harlow Shapley Discovered size of out galaxy, like other nebulae Heber Curtis Spiral nebulae are galaxies in themselves Earl Rosse had believed they were Kant's Island Universes 3. Who won the Great Debate? o Before the debate Curtis was more experienced, much better speaker Shapley was typical physicist, and terrified o Curtis fed Shapley's fear o Curtis came out ahead Although evidence was still inconclusive Russell (as in HR diagram) wrote Shapley should teach lecture course 4. How was the spiral nebulae question resolved? o Did the Great Debate solve things? No- "much heat but little light" o How does science progress? Evidence, experiment, measurement 5. The Expanding Universe in Our Understanding o Aristotle's world view Earth at the center of a series of celestrial spheres Some dissent - Aristarchus claimed the Earth moves around the sun o Kapteyn's Galaxy
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Unformatted text preview: • Modern views of solar system • Solar system at center of galaxy • Diameter of 55,ooo llightyears o Shapley's Galaxy • Diameter 300,000 lightyrs (2x too large) • Earth no longer at center • Spiral nebulae are within our galaxy o Hubble's universe • Spiral nebulae are distinct galaxies 6. Distances to galaxies o Identify cepheid o Measure brightness and period o Read off luminosity using period o Combine brightness and luminosity to get distance 7. Galaxies are moving away from us o First noted in 1914 o 11/15 spiral nebulae were red shifted o Curtis used this as evidence that they were outside the galaxy o Fully established by Hubble and Humason in 1929 • Measured red shifts and Cepheid distances for many galaxies 8. The Hubble Law o Further galaxies move faster o Hubbles original data very poor • Only nearby galaxies • Distances were inaccurate o Confirmed by modern data v=H d o Big question: What is the constant H ??...
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