IC 1318B is the Butterfly Nebula, a luminous wing of hydrogen in the heart of Cygnus. It is one bright piece of the Gamma Cygni Nebula, also called the Sadr Region, where the Milky Way runs through the Northern Cross.
Ultraviolet light from a hot, dust-hidden massive star sets the hydrogen glowing. The light is strongest in the deep red of hydrogen-alpha, crossed by threads of dark dust. The widest of those threads is LDN 889, a lane about 20 light-years thick that lies between IC 1318B and IC 1318C. The two wings are one cloud, parted on the sky by that dust, and the split draws the butterfly’s outline.
Sadr (Gamma Cygni) hangs nearby at magnitude 2.2, the star at the Swan’s chest. It is a yellow-white supergiant about 1,800 light-years away, in the foreground of this field. The nebula itself belongs to the Cygnus X star-forming complex, about 4,600 light-years from Earth, along the Orion Arm. IC 1318B covers 45 by 30 arcminutes and, at that distance, about 60 by 40 light-years. The bright clouds of the surrounding Sadr Region stretch well over 100 light-years.
Facts
- Emission nebula in Cygnus, the western wing of the Butterfly in the Sadr Region (IC 1318)
- About 4,600 light-years away, in the Cygnus X star-forming complex
- About 60 × 40 light-years across, spanning 45′ × 30′ on the sky
- J2000 position: 20h 27m 54s, +40° 00′
- Dark lane LDN 889, about 20 light-years thick, divides it from IC 1318C
- Sadr, magnitude 2.2, is a foreground supergiant about 1,800 light-years away
