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 starSigma 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 nebulaIC 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.