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Designations:
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Horsehead Nebula (Barnard 33 in bright nebula IC 434)
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Object Type:
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Dark Nebula
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Constellation:
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Orion
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05 hr 41 min 0.0 sec (Epoch 2000)
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02° 23 min 59 sec (Epoch 2000)
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Size:
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About 5 arcminutes
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Designations:
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Flame Nebula, NGC 2024
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Object Type:
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Constellation:
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Orion
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05 hr 41 min 54 sec
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+01° 51 min 00 sec
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Size:
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~30 arcminutes
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The Horsehead Nebula (Barnard 33) is one of the most photographed but least
observed objects in the sky. It is incredibly challenging for visual observers, and until rather recently
it was a prize worth crowing about even among photographers. The blob of darkness lies halfway along the
streamer of faint nebulosity that runs for 1 degree south from Zeta Orionis, the easternmost belt star. The
streamer IC434 (the abbreviation IC stands for Index Catalogue, and supplement to the New General Catalogue
of Nebulae and Clusters of Stars by J.L.E.Dreyer), is a bit brighter than the Veil Nebula in Cygnus, and no
great feat to see. But recognizing the dark blotch B33 is another matter. The Horsehead was first photographed
about 1900, but was believed to be only a void in IC 434. Barnard appears to have been the first person to
suggest that it was actually an obscuring cloud of material seen in silhouette. Deep-sky observers disagreed
on its visibility in amateur telescopes. The Horsehead is harder to see by far than the nebula around R
Monocerotis (Hubble's Variable Nebula). It is much harder than the veil in Cygnus or spiral
galaxy M33 in
Triangulum. Possibly it is more difficult than the Merope Nebula in the Pleiades. In any case, the observer
should wait for special weather and use a photograph as a detailed finder chart. Scattered light from 2nd-
magnitude
Zeta foils may attempts to find the Horsehead, since the two are separated by only 1/2 degree. Another reason
that many searches fail is that observers are looking for the wrong-sized object. When seen in telescopes
between 10 and 16 inches in aperture, it always appears very tiny. Knowing just where to look is half the battle.
The Horsehead is only about 5
arcminutes
across. Amateurs accustomed to seeing it on large-scale photographs made with
professional telescopes end up looking for an object that is much too big.
Of course, the Flame Nebula is not on fire. Also known as NGC 2024, the nebula's suggestive reddish color is due to the glow of hydrogen atoms at the edge of the giant Orion molecular cloud complex some 1,500 light-years away. The hydrogen atoms have been ionized, or stripped of their electrons, and glow as the atoms and electrons recombine. But what ionizes the hydrogen atoms? In this close-up view, a dark lane of absorbing interstellar dust stands out in silhouette against the hydrogen glow and actually hides the true source of the Flame Nebula's energy from optical telescopes. Behind the dark lane lies a cluster of hot, young stars, seen at infrared wavelengths through the obscuring dust. A young, massive star in that cluster is the likely source of energetic ultraviolet radiation that ionizes the hydrogen gas in the Flame Nebula. The description of the Flame Nebula was written by the authors of Astronomy picture of the day http://apod.nasa.gov |
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Telescope:
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Focal Length:
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384mm (480mm with 0.8X reducer)
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Mount:
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Camera
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Guider:
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Exposures:
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18 10-Minute Exposures through a Hydrogen-Alpha filter
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Location:
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Cicero, IN
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Software:
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CCDSoft for image acquisition, processed with CCDStack and Photoshop CS2
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