The bright star at the heart of Cygnus is Sadr (Gamma Cygni), the crossing point of the Northern Cross. Around it spreads the Sadr Region, an emission nebula catalogued as IC 1318 and also called the Gamma Cygni Nebula. In this stretch of the Milky Way, ultraviolet light from young stars ionizes hydrogen, and the gas shines; dark dust lanes cut that glow into separate clouds.
Sadr is a yellow-white supergiant of spectral type F8 Iab, magnitude 2.23, about 1,800 light-years away. Its name, from the Arabic ṣadr, means “chest”: the breast of the Swan. The nebula lies farther along the same line of sight, in the Cygnus X star-forming complex, about 5,000 light-years from Earth. At that distance the visible gas covers more than 100 light-years.
The complex breaks into three bright masses, IC 1318 A, B, and C. A dark cloud, LDN 889, about 20 light-years thick, runs between the southern pair and gives them the wing-like outline sometimes called the Butterfly Nebula. These photographs frame that field: the supergiant in front, and the red hydrogen and carved dust of IC 1318 behind it.
Facts
- Emission nebula (H II region) in Cygnus, on the plane of the Milky Way
- About 5,000 light-years away, and more than 100 light-years across
- Sadr is a foreground F8 Iab supergiant, magnitude 2.23, about 1,800 light-years away
- The name Sadr is Arabic for “chest,” the heart of the Swan and the center of the Northern Cross
- Bright clouds IC 1318 A, B, and C, with the dark nebula LDN 889 between B and C
- Sky position near right ascension 20h 22m, declination +40° 15′
