What fundamentally distinguishes a dark nebula from a bright nebula like the Flame Nebula?

Answer

A dark nebula is a dense, opaque concentration of dust that physically blocks the light from sources behind it.

Dark nebulae, such as Barnard 33, are characterized by dense clouds of interstellar dust composed of silicate or carbon-based particles that absorb and scatter visible light, creating shadows against brighter objects.

What fundamentally distinguishes a dark nebula from a bright nebula like the Flame Nebula?
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