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Witch Head Nebula

IC 2118

Proper NameWitch Head Nebula
NGC/IC NumberIC 2118
Right Ascension5h 2m 0s
Declination-7° 54' 0"
Distance962 light years
295 parsecs
DimensionsApparent: 3° x 1°
Actual diameter: 39 light years
Optimum VisibilityDecember

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 Witch Head Nebula in northern Eridanus lies close to the feet of Orion (and indeed within the asterism known as Orion's Footstool). The bright star visible in the southeastern corner of this image is Rigel in Orion, whose light illuminates the gases of the nebula. Imagery provided by Aladin sky atlas

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 supergiant star Rigel in Orion, and the nature of the particles within the nebula cause it to reflect this light with a characteristic blue-violet colour.


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