How is the cloud-like appearance of a dark nebula primarily defined?

Answer

By dense, opaque dust obscuring visible light from sources behind it

Dark nebulae are defined by their opacity; they are dense concentrations of material so thick that they create a silhouette against brighter objects lying in the background.

How is the cloud-like appearance of a dark nebula primarily defined?

#Videos

Nebulae: Crash Course Astronomy #36 - YouTube

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