What celestial objects were sometimes classified as 'nebulae' historically due to their fuzzy appearance?

Answer

Distant galaxies, like the Andromeda Galaxy

Historically, the term nebula was applied broadly to any fuzzy patch of light; modern technology later differentiated these distant stellar collections (galaxies) from true interstellar clouds.

What celestial objects were sometimes classified as 'nebulae' historically due to their fuzzy appearance?
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