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1755: Philosopher Immanuel Kant proposes the universe is filled with great wheels of stars - ‘island universes’ 1845: William Parsons identifies ‘spiral nebulae’. The Great Debate (1920):.
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1755: Philosopher Immanuel Kant proposes the universe is filled with great wheels of stars - ‘island universes’ 1845: William Parsons identifies ‘spiral nebulae’
The Great Debate (1920): Harlow Shapley argued that the "spiral nebulae" were nearby gas clouds, and that the Universe was composed of only one big Galaxy. Heber D. Curtis argued that the universe is composed of many galaxies like our own • 1924: Edwin Hubble measures distances to the brightest spiral • nebulae • Supergiant stars in the spiral nebulae are so faint that they must be • far outside the Milky Way
Spiral Galaxies,.... ...elliptical galaxies,... ... and irregular galaxies
Galaxy Clusters and Large Scale Structure Virgo Cluster
A few hundred billion galaxies can be seen with • current telescopes • Sloan digital sky survey has mapped out the distribution of • galaxies in certain parts of the sky
Olber’s Paradox (1826) Why is the night sky dark?
Olber’s Paradox (1926) Why is the night sky dark?
Olber’s Paradox Why is the night sky dark? • The universe has an edge • The stars and galaxies ‘run out’ at some distance from us • The universe has a beginning First suggested by Edgar Alllen Poe in 1848