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Cave Nebula

C9, Sh2-155

Proper NamesFly Nebula
Messier NumberNone
NGC/IC NumberNGC 1931
Right Ascension5h 32m 19s
Declination+34° 12'
Distancec.7,000 light years
c.2,100 parsecs
Mean DiameterApparent: 4°
Actual: c.10 light years
Optimum VisibilityDecember/January
NotesAn area of nebulosity some seventy light years from side to side, much of this bright emission nebula is obscured by a borad dark cloud so that, as seen from Earth, it appears as a ragged arc of light reminiscent of a cave's mouth.