MPIA-HD, BIRKLE, SLAWIK / SCIENCE PHOTO LIBRARY MPIA-HD, BIRKLE, SLAWIK / SCIENCE PHOTO LIBRARY
Horsehead Nebula. Optical image of Barnard 33 (the Horsehead Nebula), 1600 light years away in the constellation of Orion. North is at left. The horsehead shape is formed by an intrusion of dust into the emission nebula IC 434. The red glow from this nebula is due to the ionisation of hydrogen by radiation from nearby stars. A reflection nebula (blue, NGC 2023) is at lower left.
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