Why might a dark nebula become almost invisible if viewed against the emptiness of deep space?
Answer
Its visibility is context-dependent, relying entirely on contrast provided by a bright background, such as the plane of the Milky Way.
The defining feature of a dark nebula is its ability to obscure light sources behind it, meaning its visibility is inherently relative to what lies beyond it. If a dark nebula is observed against the vast emptiness of deep space, where there is no luminous source or background emission to block, it effectively blends into the blackness and becomes functionally invisible. Its standout appearance is purely a result of contrast against a luminous backdrop, such as the dense band of stars and glowing gas making up the Milky Way galaxy.
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