Announcements

1
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!

2
Galaxies

• 17 November 2006

3
Today

• The spiral nebulae
• Measuring distances to galaxies
• Rotation rates and dark matter

4
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

5
The Discovery of Spiral Structure
Lord Rosse, 1845
6
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

7
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
8
Finding the Andromeda Galaxy
9
Finding the Andromeda Galaxy
10
Finding the Andromeda Galaxy
11
Finding the Andromeda Galaxy
12
The Andromeda Galaxy
13
The Andromeda Galaxy
14
The Andromeda Galaxy
15
The Magellanic Clouds
16
Hubble Space Telescope can detect Cepheids out to
60 million light-years (Virgo Cluster)
17
Virgo Cluster
18
NGC 253
19
Whirlpool Galaxy (M51)
20
M83
21
M104 (Sombrero Galaxy)
22
Edge-on galaxies
23
Barred spiral galaxies
24
Colliding Galaxies
25
Galaxy with dust lane
26
Group of galaxies in Leo
27
Beyond 50 million light-years, the best standard
candles are type-I supernovas
28
Coma Cluster
29
Coma Cluster
30
Hubble Deep Field