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Omega Nebula

Checkmark Nebula, Horseshoe Nebula, Swan Nebula,
M17, NGC 6618

Proper NamesOmega Nebula, Checkmark Nebula, Horseshoe Nebula, Swan Nebula
Messier NumberM17
NGC/IC NumberNGC 6618
Right Ascension18h 20m 47s
Declination-16° 10' 18"
Distancec.5,500 light years
c.1,700 parsecs
MagnitudeApparent: +6.0
Absolute: -4.6
Mean DiameterApparent: 46' x 37'
Actual: 20-30 light years
Optimum VisibilityJuly

Part of a dense concentration of nebulae and star clusters scattered across the sky in the direction of the Galaxy's core as the Milky Way passes through Sagittarius. The Omega Nebula lies southward of M16, the famous Eagle Nebula in Serpens, though the two nebulae are not physically connected (the Eagle Nebula lies several hundred light years beyond the Omega Nebula).

The visible Omega Nebula is actually a part of a much larger cloud of material some forty light years in diameter. Much of this material is dark, but in its heart is a star-forming region some fifteen light years across. New stars coming to life there, notably the cluster NGC 6618, illuminate the surrounding gas and dust.

This brighter region appears to form a narrow looping shape with an angled tail, like a rather elongated Greek letter Omega, from which the nebula takes its most common name. The same shape can be - with imagination - interpreted as a swan in flight, a horseshoe, or a checkmark, all of which have been used as alternative proper names. These structures stand out more clearly at lower resolutions - in more detailed images of the nebula, these shapes tend to be rather less obvious.


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