Galactic Nebula Sh 2-9
History
Who first discovered the nebula around the star σ Scorpii is unclear. As early as 1920, Seares and Hubble examined the spectrum of this «nebulous star». [564] In 1955, the Australian astronomer Colin Stanley Gum listed the nebula around σ Scorpii as the 65th object (Gum 65) in his «Survey of Southern HII Regions». [555] In the late 1950s, the American astronomer Stewart Sharpless classified the large nebula Sh 2-9 as an H-II region on the basis of the photographic plates of the «Palomar Observatory Sky Survey». In 1959, he published his discovery in a catalogue along with 313 HII regions. [310]
Physical Properties
Sh 2-9 (Sharpless 2-9) is a reflection and emission nebula around the 2.9 mag bright star σ Scorpii (Al Niyat). The reddish areas consist of ionised hydrogen and are excited to glow by the star's UV radiation. The bluish ones are dust reflecting the star's light. This nebula belongs together with IC 4603, IC 4604, IC 4605 the Antares Nebula vdB 107 and many dark clouds to form a large nebula area, the Ophiuchus Molecular Cloud. Its centre lies about one degree south of the star ρ Ophiuchi, is surrounded by dense dust and is only visible on infrared images.
The Ophiuchus Molecular Cloud, also called the Rho Ophiuchus Cloud, is an area of active star formation that is one of the closest to us, at a distance of only about 407 light years. X-ray and infrared observations have revealed more than 300 young stars within the large cloud at its centre. The age of these stars is estimated to be only 300'000 years - very young compared to the oldest stars in the universe, which are more than twelve billion years old. [460]
Finder Chart
The nebula Sh 2-9 is located in the constellation Scorpius around the 2.9 mag bright star σ Scorpii (Al Niyat). On 27 May it is in opposition to the Sun and culminates at local midnight. The best time to observe is April to August.
