types of galaxies spirals (77%) ellipticals (20%) irregulars (3%) national optical astronomy...
TRANSCRIPT
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GALAXIES
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Types of GalaxiesSpirals (77%) Ellipticals (20%) Irregulars (3%)
National Optical Astronomy Observatory images
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Galaxy types: Spirals
a: NASA/Hubble Space Institute; b: Robert Gendler; c: Anglo-Australian Observatory
• spiral disk shape with arms
• central nuclear bulge
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Spiral galaxies – side view
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Spirals – top view
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Spiral arms don’t wind up
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Ripples in rotating water/gas/dust form spiral arms
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Galaxy Types: Barred Spirals
• central bulge is elongated, like a bar
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The Milky Way
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Galaxy Types: Elliptical
(a) NASA; (b) RoyalObservatory, Edinburgh
• no spiral shape or arms
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Elliptical Galaxy Variations
a: J. D. Wray, McDonald Observatory; b, c: 1999 Princeton University Press/Zsolt Frei and James E. Gunn
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• neither spiral nor elliptical
• white & dusty
Galaxy Type: Irregular
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Edwin Hubble(1889-1953)
Milton Humason
(1891-1972)
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Hubble’s Classification System
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Cosmic Distance Ladder
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Hubble’s Law:
Velocity of Distant Galaxies Increases with Distance
Closer Galaxies move away from us
Farther Galaxies move away from us faster
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Hubble’s Constant yields Age of Universe
Hubble’s Constant Tells Age:
H0 = Velocity/Distance = 1 / Time
Hubble’s Law:
Velocity = H0 x Distance
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The Local Group
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Neighborhood Superclusters
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Large Scale Structure in the Universe
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Colliding Galaxies
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Gravitational Lenses and Dark Matter
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