This image contains several distinct features.
NGC 6910 – Inchworm Cluster / Rocking Horse Cluster. It is a small open cluster located near Gamma Cygni (Sadr) in the constellation of Cygnus. It lies approximately 3700 light years away, near the galactic plane. It is embedded in IC 1316, a much larger emission nebula.
Sadr, Gamma Cygni (γ Cyg) is a yellow-white supergiant star. With an apparent magnitude of 2.23, it is the constellation’s second brightest star, after Deneb. Sadr lies at an approximate distance of 1,800 light years from Earth. It is the star that marks the intersection of the Northern Cross, a bright asterism that dominates the summer sky in the northern hemisphere. Sadr lies in a rich field of the Milky Way and is surrounded by the diffuse emission nebula IC 1318, also known as the Gamma Cygni Nebula or Sadr Region.
IC 1318 – Sadr is surrounded by the emission nebula IC 1318, one of the several nebulous regions at the centre of the Northern Cross. IC 1318 is known as the Gamma Cygni Nebula, Sadr Region or the Butterfly Nebula. It is not physically related to Sadr, but merely lies in the same line of sight. The nebula is located much farther away than the star, at a distance of 4,900 light years. The star that illuminates IC 1318 is a hot, blue O9-class star obscured by interstellar dust.
Sadr is the central star of the Northern Cross, also formed by the bright Deneb (Alpha Cygni), Albireo (Beta Cygni), Aljanah (Epsilon Cygni) and Fawaris (Delta Cygni). Deneb, Sadr and Albireo form the pole of the cross, while Aljanah and Fawaris mark the crossbeam.
The name Sadr (pronunciation: /ˈsædər/) comes from the Arabic ṣadr, meaning “chest.” It has the same etymology as the name of Alpha Cassiopeiae, Schedar. The name has also been spelled Sadir or Sador. It refers to the star’s position in the constellation, marking the Swan’s chest. The name was officially approved by the International Astronomical Union’s (IAU) Working Group on Star Names (WGSN) on August 21, 2016. It formally applies only to Gamma Cygni A.
Sadr is very easy to find because it lies at the intersection of the bright, large Northern Cross asterism. The Northern Cross is easy to spot on a clear night. It lies within the larger Summer Triangle, a brighter summer asterism formed by Deneb with Vega in the constellation Lyra and Altair in Aquila.
Sadr is located in the vicinity of several interesting deep sky objects. The Rocking Horse Cluster (NGC 6910) is an open cluster located only half a degree east and a little north of the star. It is at a similar distance as the Gamma Cygni Nebula and may be physically associated with it. The cluster has an apparent magnitude of 7.4 and occupies an area of 10’. The neighbouring open cluster Collinder 419 (Cr 419) is only slightly fainter, with a visual magnitude of 7.60.
Sadr is located in the constellation Cygnus. Representing the celestial Swan, Cygnus is one of the larger northern constellations, stretching across 804 square degrees of the apparent sky. It is known mainly for the Northern Cross and its bright stars Deneb, the 19th brightest star in the sky, and Albireo, a famous contrasting double.
The constellation contains a number of well-known deep sky objects, among others the bright open clusters Messier 29, Messier 39 and NGC 6910, the Fireworks Galaxy (NGC 6946), and several bright nebulae, including the North America Nebula (NGC 7000), the Pelican Nebula (IC 5070), the Veil Nebula (NGC 6960, 6962, 6979, 6992 and 6995), the blinking planetary nebula (NGC 6826), and the nebulae near Sadr: the Gamma Cygni Nebula (IC 1318) and the Crescent Nebula (NGC 6888).
The best time of year to see the stars and deep sky objects in the constellation is during the month of September.
Key Facts & Summary
Sadr is located at around 1,800 light-years / 560 parsecs away from the Sun.
Sadr is the second brightest star in the constellation of Cygnus, after Deneb. This star is also among the brightest stars in the night sky.
Its location marks the intersection of the Northern Cross, a bright asterism that dominates the summer sky in the northern hemisphere.
In comparison to our Sun, Sadr is around 33,023 times brighter, yet it is several times younger, having an estimated age of around 12 million years.
Sadr has around 12.11 solar masses and a radius of 150 times that of our Sun.
Sadr is a supergiant star of spectral type FB8 lab, appearing yellowish-white in color.
The star is surrounded by a diffuse nebula called IC 1318, or the Gamma Cygni region.
The star’s name, Sadr, is derived from Arabic and it translates to “chest.” The same word gave rise to the name of the star Schedar – Alpha Cassiopeiae.
Sadr formed at around 12 million years ago from an interstellar medium of gas and dust. Gravity pulled the swirling gas and dust together until it reached the critical temperature, giving birth to the second-brightest star in Cygnus, named Sadr.
It is quite a young star and the interstellar medium from which it was born was probably abundant in elements such as hydrogen, thus the reason for its short lifespan, as Sadr will eventually go supernova.
Sadr has reached the supergiant stage of its stellar evolution and thus its radius has expanded and it will probably continue to expand several times its former size.
Since Sadr is so massive, it will one day go supernova and illuminate a big portion of the night sky, despite being such a young star.
