Nebular Taxonomy.

1
Nebular Taxonomy.

• Planetary nebulae.
• Diffuse nebulae
• Gaseous, glowing (Crab--SN1054)
• Dusty, absorbing (Horsehead)
• Star Clusters
• Open clusters (M44)
• Globular Clusters (M13 in Hercules, M22 in
  Sagittarius)
• Extragalactic nebulae
• Spirals (Andromeda, Whirpool)
• Ellipticals (M87)
• Irregulars (M82)

2
What are the Spiral Nebulae?

• Nature of the Milky Way
• A flattened disk of stars.
• Thomas Wright (1750) Immanuel Kant (1755)
  Johann Lambert (1761)
• Solar system in the far-distant suburbs (Shapley,
  1918).
• Spiral Nebulae as Island Universes? (Kant, 1755)
  
• Great Debate (April 26, 1920)
• Harlow Shapley Spiral Nebulae within the Milky
  Way.
• Heber Curtis Spiral Nebulae external island
  universes ala Kant.
• Andromeda is a distant island universe (2
  Mlt-yr). Edwin Hubble Jan. 1, 1925. (Most
  distant object visible to the naked eye).