Selection Effects

• Catalog used by Persic and Salucci composed of objects bright and large enough to be detected through the noise of the night sky

• Sky brightness limits the objects we can view to a narrow band of apparent brightness (magnitude)

  

  • Sky Brightness from:
    Sunlight
    Moonlight
    Terrestrial Light
    Light from stellar & extragalactic objects

• 1965 Arp quantified the effect of sky brightness:
  

  These effects can be quantified by the idea of surface brightness.