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IC 434

Proper NameAssociated with the Horsehead Nebula
NGC/IC NumberIC 434
Right Ascension5h 41m 0s
Declination-2° 30' 0"
Distancec.1,500 light years
c.460 parsecs
DimensionsApparent: 1° 30' x 30'
Actual: c. 40 x 14 light years
Optimum VisibilityDecember / January
NotesA long thin strand of nebulous material stretching southwards for a degree across the sky (about twice the diameter of the Moon's disc) from the region around Alnitak, the easternmost of the three stars that make up Orion's Belt.

A long thin nebulous region running north to south near Alnitak, the eastern star of Orion's Belt. IC 434 is far better known than its Index Catalogue number might suggest - it is the bright background nebula against which the famous dark region called the Horsehead stands out.

IC 434 is the bright ribbon of nebulous material running vertically through this image. The bright star to the west (or right) is Sigma Orionis, whose energy makes the nebula visible. The brilliant star on the northern edge of this image is Alnitak, the eastern of the three stars that make up Orion's Belt. Imagery provided by Aladin sky atlas

The constellation of Orion is home to the Orion Molecular Cloud, an immense complex of dark nebulae. For the most part the structure of this nebula complex is only barely detectable in visible light, but in certain regions local conditions cause patterns within the cloud to shine against their dark background.

This is the case with IC 434, which lies within the vast southern lobe of the cloud complex. The nebula represents the outer boundary of a cloud of ionised hydrogen illuminated by the star Sigma Orionis to the west. Eastward beyond this curtain of material lies a dark nebula obscuring the light of the stars behind it, so that IC 434 appears to have a relatively sharp eastern boundary. Magnetic forces within the cloud complex cause streamers of material to erupt from the main nebulous mass, appearing as faint tendrils extending out at a perpendicular angle to the linear shape of the main nebula.

At one point, about halfway along the length of IC 434, the dark cloud to the east extends a narrow, twisted branch to break the otherwise smooth line of the background nebula IC 434. This twisting curl of dark material is some three light years from end to end, and its angle as seen from Earth gives it the unmistakable shape from which it takes its name, the Horsehead Nebula.


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