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Announcements. 4th test is finished! Please pick up graded work Homework 12 due Monday (requires internet use) Second project is due in two weeks Please reread lyrics to Monty Python galaxy song; document the inconsistency for a free Milky Way bar!. Galaxies. 17 November 2006. Today :.

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Announcements

  • 4th test is finished!

  • Please pick up graded work

  • Homework 12 due Monday (requires internet use)

  • Second project is due in two weeks

  • Please reread lyrics to Monty Python galaxy song; document the inconsistency for a free Milky Way bar!


Galaxies

17 November 2006


Today:

  • The “spiral nebulae”

  • Measuring distances to galaxies

  • Rotation rates and “dark matter”


Messier Catalog

  • 27 “open” clusters

  • 29 globular clusters

  • 6 diffuse nebulae

  • 4 planetary nebulae

  • 1 supernova remnant

  • 2 small groups of stars

  • 40 other fuzzy things in which no individual stars are visible


The Discovery of Spiral Structure

Lord Rosse, 1845


What are the spiral and elliptical nebulae?

  • No individual stars are visible, even in largest telescopes

  • Some have spiral structure, as if spinning rapidly

  • Visible amount of rotation over a few decades?

  • Continuous spectra

  • Hypothesis 1: Swirling clouds of fluid, possibly forming new solar systems

  • Hypothesis 2: “Island universes,” similar to our own Milky Way star system


Island Universes Confirmed!

Edwin Hubble discovers Cepheid variable stars in the Andromeda Nebula, 1923

Estimated distance: 1 million light-years (actually 2 million)

Edwin Hubble, 1889 - 1953


Finding the Andromeda Galaxy


Finding the Andromeda Galaxy


Finding the Andromeda Galaxy


Finding the Andromeda Galaxy


The Andromeda Galaxy


The Andromeda Galaxy


The Andromeda Galaxy


The Magellanic Clouds


Hubble Space Telescope can detect Cepheids out to 60 million light-years (Virgo Cluster)


Virgo Cluster


NGC 253


Whirlpool Galaxy (M51)


M83


M104 (Sombrero Galaxy)


Edge-on galaxies


Barred spiral galaxies


Colliding Galaxies


Galaxy with dust lane


Group of galaxies in Leo


Beyond 50 million light-years, the best standard candles are type-I supernovas


Coma Cluster


Coma Cluster


Hubble Deep Field


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