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This curious dark nebula is one of the best-known images in astronomy, probably because of its chance likeness to a recognisable form. The horse-head shape is an extension of a large cloud of dust which fills the lower part (east) of the picture and hides the light of stars beyond. The outer surface of the dusty gas (IC 434) runs roughly north-south and is illuminated by sigma Orionis (off the top of the picture) which causes the hydrogen there to fluoresce, outlining the horse-head shape. Though conspicuous here, the Horsehead is very difficult to see visualy, eben with a large telescope. A bright star is partially enveloped in the dust cloud and its scattered light is seen as the large, irregular blue reflection nebula, NGC 2023.
Image and text copyright © Anglo-Australian Observatory. All rights reserved. Photograph by David Malin. |
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