Galaxies
What Are Galaxies?
• Greek galax = milk
• William Herschel, 1783: A disk with the Sun
slightly off-center
What Are Galaxies?
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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
Galaxies and Globular Clusters
The Milky Way’s Globular Clusters
The Milky Way As We See It
The Visual
Milky Way
Anatomy of a Galaxy
Spiral Arms
In Microwaves, We Can See the Hub
of the Galaxy
Center of the Milky Way
The Galaxy
Mapping the Neighborhood
Mapping the Neighborhood
Mapping
the
Galaxy:
Not There
Yet
Mapping
the
Galaxy:
Not There
Yet
Hubble’s Classification of Galaxies
Elliptical
Galaxy
(M87)
S0/Sa Galaxy
Barred S0 Galaxy
Sa Galaxy (Seyfert)
Sb Galaxy (M81)
M81 in Ultraviolet
Sc Galaxy
Sc Galaxy
Sc Galaxy (M51)
Sba Galaxy
SBb Galaxy
SBc Galaxy
Density Waves
Rotation of the Milky Way
Ring Galaxy
Ring Galaxy
The
Local
Group
Downtown: The Virgo Cluster: 50
m.l.y
The
Local
Supercluster
The Coma
Cluster
350 m.l.y.
Large-Scale
Structure of
the
Universe to
500 m.l.y.
Large-Scale Structure of the
Universe