A long, narrow reflection nebula in northern Eridanus that stretches for some three degrees from end to end in the sky, making it comparable in angular size with Orion's Belt (this angular distance translates to an actual length of some forty light years). With a visual magnitude of just +10, however, the nebula is far too faint to be seen with the naked eye. Undulations along its eastern edge resemble a face in profile, with a long pointed nose and an open mouth, hence its common name of the 'Witch Head Nebula'. This resemblance stands out much more clearly if the nebula is seen inverted, as it appears in an optical telescope.
The structure of the nebula suggests that it originated as the remnant of a supernova in the very distant past. Within the nebula are molecular clouds dense enough to give rise to another generation of star formation within its material (this effect is amplified by the interaction of the expanding supernova remnant with molecular clouds expanding outwards from the stars of Orion). The nebula does not shine by its own light, but reflects that of the nearby supergiantstarRigel in Orion, and the nature of the particles within the nebula cause it to reflect this light with a characteristic blue-violet colour.