Starting Ch.9: Interstellar Medium
• Since stars die, new ones must somehow be born
• They must be made out of material like star:
– H, He, plus a little heavier elements
• Three types of interstellar “nebulae” or clouds
– Emission nebulae   -- Glow with emission lines
– Reflection nebulae   -- Reflect starlight
– Dark nebulae     -- seen in silhouette