ay45c1-page3 - f ) Astronomy and astrophysics generally...

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Unformatted text preview: f ) Astronomy and astrophysics generally assumes the Copernican principle: WE ARE IN NO FAVORED POSITION IN THE UNIVERSE. so the Universe near us and physics near us are typical of contemporaneous parts of the Universe | unless, of course, we nd factual evidence to the contrary (and this should be, in each such case, only by rare good or bad luck.) When does astronomy turn into astrophysics? No hard-and-fast line, but where physical laws (not just geometric arguments or logic) are applied. 1.2 Quick history of some pre-astrophysics discoveries 1.2.1 Copernicus gets Solar System geometry, but no scale Copernicus (early 1500's!) measured the relative size of the planetary orbits to  1%. His unit, the astronomical unit (AU), was of unknown size. The technique was geometry: Quadrature Elongation (~30 ) Opposition Inferior conjunction Greatest eastern elongation Earth Sun Quadrature East Earth Conjunction Sun Greatest western elongation Superior conjunction East If one assumes circular orbits and constant velocities along orbits (can check this observationally), then the dates of opposition/quadrature/greatest elongation/conjunction give the relative geometry. 3 ...
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