The Sadr region, or IC 1318, is the diffuse emission nebula surrounding Sadr or Gamma Cygni. Sadr lies in the center of Cygnus’s cross.
What is the Sadr region?
The Sadr region is one of the surrounding nebulous regions; others include the Butterfly Nebula and the Crescent Nebula. It contains many dark nebulae in addition to the emission diffuse nebulae. The nebulous regions around the region are also fairly bright.
Gamma Cygni, also named Sadr, is a star in the northern constellation of Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. Compared to the Sun this is an enormous star, with 12 times the Sun’s mass and about 150 times the Sun’s radius. It is emitting over 33,000 times as much energy as the Sun, at an effective temperature of 6,100 K in its outer envelope.
A dark nebula or absorption nebula is a type of interstellar cloud that is so dense that it obscures the light from objects behind it, such as background stars and emission or reflection nebulae. The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules. Like other interstellar dust or material, things it obscures are only visible using radio waves in radio astronomy or infrared in infrared astronomy.
The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The largest dark nebulae are visible to the naked eye, appearing as dark patches against the brighter background of the Milky Way like the Coalsack Nebula and the Great Rift. These naked-eye objects are sometimes known as dark cloud constellations and take on a variety of names.
Image: Erik Larsen
Text: Wikipedia contributors. “Sadr Region.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 21 Jun. 2017. Web. 9 Aug. 2017. & Wikipedia contributors. “Gamma Cygni.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 21 Jun. 2017. Web. 9 Aug. 2017. & Wikipedia contributors. “Dark nebula.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 9 Apr. 2017. Web. 9 Aug. 2017.