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IC 1318 is a giant HII region and one of the brightest among all the emission clouds in the Cygnus complex. The visible HII region spans over 100 light years. The bright star projected in the center of the nebulosity is a class F8 star known as Sadr or Gamma Cygni. Its true location is only 750 light years away and not related to the nebulosity which is much more distant at 5000 light years. There is considerable obscuration of the region due to intervening dust within the great rift of the Milky Way which attenuates the light of many of the bright stars spread through the region. The great rift represents a series of overlapping dark clouds that create a division in the Milky Way between the Cygnus and Sagittarius star clouds.
The entire nebula complex referred to as IC 1318 has three distinct visible components, IC1318 a, b, and c. IC 1318 b and c constitute a single giant HII cloud bisected by a thick obscuring dust lane known as LDN 889. The two components (b and c) of the HII region straddle the thick dust lane along its northern and southern borders. The symmetry of the complex has been compared to a butterfly which has led to its popular name as the "Butterfly Nebula". The bisecting dust lane is 20 light years thick and is physically bound to the emission nebula and its parent molecular cloud complex. The entire HII region is illuminated by a solitary visually obscured class O9 star. The area is complex and several unrelated nebulae are projected together in the same region. One of the brightest supernova remnants at radio wavelengths is projected over the same line of sight as IC 1318 but is more distant by at least another 1000 light years.
Located nearby IC 1318 and cloaked by the Great Rift of the Milky Way lies the Cygnus OB2 association at a distance of about 5500 light years. This massive grouping of young stars is arguably the most massive and extensive stellar association in the Milky Way. It contains over 2600 OB type stars spread across 200 light years of space. Its total gaseous content is estimated to be over several hundred thousand solar masses. The stars of Cygnus OB2 are quite young having formed between one and two million years ago. The obscuration and reddening of the association by the thick obscuring dust of the region has hampered an accurate account of all its members. Its unusually massive and compact nature has led some astronomers to suggest it could be cataloged as a globular cluster rather than an OB association. Some astronomers have suggested that Cygnus OB2 be considered a super star cluster similar to 30 Doradus in the Large Magellanic Cloud. More detailed infrared studies should help to uncover massive star clusters hidden from view by the dust of our galaxy.
Distance: 5000 Light Years
Right Ascension: 20 : 22.2 (hours : minutes)
Declination: +40 : 15 (degrees : minutes)
Image & Text Copyright Robert Gendler