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Galaxies. What Are Galaxies?. Greek galax = milk William Herschel, 1783: A disk with the Sun slightly off-center. What Are Galaxies?. 19th Century: “Spiral Nebulae” Nearby? Maybe Solar Systems in Formation? 1920: Galaxies are Stars 1920’s: Galaxies are like the Milky Way
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What Are Galaxies? • Greek galax = milk • William Herschel, 1783: A disk with the Sun slightly off-center
What Are Galaxies? • 19th Century: “Spiral Nebulae” • Nearby? Maybe Solar Systems in Formation? • 1920: Galaxies are Stars • 1920’s: Galaxies are like the Milky Way • Biggest single increase in our mental picture of the Universe in human history
Where Are We in our Galaxy? • The visible Milky Way suggests our galaxy is a flat disk • Surrounding other galaxies is a spherical halo of Globular Star Clusters