Study Guide for Quiz 3:
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The Cosmic Distance Problem
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  Trigonometric Parallaxes
  Luminosity Distances
    "Standard Candles"
    Spectroscopic Parallaxes
  Cepheid Variables
  Period-Luminosity Relation
  RR Lyrae Variables

The Milky Way Galaxy
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  The Milky Way is our Galaxy
    Diffuse band of light crossing the sky
    Galileo: Milky Way consists of many faint stars
  The Nature of the Milky Way
    Philosophical Speculations: Wright & Kant
  Size of the MW from
    Star Counts: Herschels Star Gauges
                 Kapteyn Model
    Globular Cluster Distribution: Shapley

Nature of the "Spiral Nebulae"
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  Two hypotheses
    Island Universe Hypothesis (Kant & Humboldt)
    Nebular Hypothesis (Laplace)
  Role of finding distances in resolving the debate
    Leavitt: Cepheid Period-Luminosity Relation
    Shapley-Curtis Debate (1920)
    Hubble: Cepheids in Andromeda

The Milky Way & Andromeda
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  Common Properties of the Milky Way & Andromeda Galaxies
  Disk & Spheroid Structure of the Galaxy
  Pop I Stars: 
    Young, metal-rich, disk stars
    Ordered, nearly circular orbits in the disk
  Pop II Stars:
    Old, metal-poor, spheroid stars
    Disordered, elliptical orbits in all directions
  Chemical Evolution
  Supermassive Blackholes

Spiral Galaxies
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  Disk & Spheroid Components
    Thick disk of stars, thin disk of dust, spiral arms
    Spheroid: bright central Bulge and faint extended Halo
  Rotation of the Disk
    Differential Rotation Pattern
    Orbital period of the Sun
    Measurement of Galaxy Masses
  Spiral Arms:
    Outlined by O&B Stars, HII Regions, Gas & Dust clouds
    Spiral Density Waves in the Disk
    Sites of recent star formation.
    Why O&B stars don't move very far from their birthplaces.

Types of Galaxies
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  Three basic types of Galaxies:
    Spirals
    Ellipticals
    Irregulars
  Hubble Classification System
    "Tuning Fork" Diagram
  Dwarf Galaxies
  Differences between the types of galaxies in terms of
    Relative Gas content
    Star Formation History
    Internal Motions

Groups & Clusters of Galaxies
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  Galaxies tend to group into Clusters
  The Milky Way is part of the Local Group
  Hierarchy of Structure:
    Groups: < 30 bright galaxies
    Clusters: 30 - 100's of bright galaxies
      Where Ellipticals & Spirals are found in Rich Clusters
    Superclusters: Clusters of Clusters
    Voids, Filaments, & Walls
  
Interacting Galaxies
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  Tidal Interactions occur between Galaxies
    Frequency of occurence
    Cause of most of the "peculiar" galaxies observed
    Tidal distortion in encounters
  Types of interactions
    Close Tidal Encounters
    Galaxy-Galaxy Collisions
    Splash encounters (Ring Galaxies)
  Starbursts induced by interactions
  Mergers & Galactic Cannibalism

Active Galaxies & Quasars
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  Found in a small fraction of all galaxies
    Compact source of energy in the nucleus
    Include the most luminous objects known
  Types:
    Quasars: Quasi-stellar Radio Sources
    Radio-Quiet Quasars (QSOs)
    Seyfert Galaxies
    Radio Galaxies
  Power source:
    Supermassive Black Holes
    Accretion Disks
    Radio Jets