Sh 2-279 (alternatively designated S279 or Sharpless 279) is an

HII region An H II region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light year ...

and bright nebulae that includes a

reflection nebula In astronomy, reflection nebulae are interstellar cloud, clouds of Cosmic dust, interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to Ionization, ionize the gas of the nebu ...

located in the constellation Orion. It is the northernmost part of the asterism known as Orion's Sword, lying 0.6° north of the

Orion Nebula The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula in the Milky Way situated south of Orion's Belt in the Orion (constellation), constellation of Orion, and is known as the middle "star" in the "sword" of Orion. It ...

. The reflection nebula embedded in Sh 2-279 is popularly known as the Running Man Nebula. Sh 2-279 comprises three NGC nebulae, NGC 1973, NGC 1975, and NGC 1977 that are divided by darker nebulous regions. It also includes the

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

NGC 1981. The brightest nebulosity, later listed as NGC 1977, was discovered by

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

in 1786. He catalogued it as "H V 30" and described "!! 42 Orionis and neb la. The two smaller reflection nebulae were first noted by German astronomer Heinrich Louis d'Arrest, NGC 1973 in 1862 and NGC 1975 in 1864. All three were included in the

New General Catalogue The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxy, galaxies, star cluste ...

in 1888. The designation NGC 1977 is used in various sources for the reflection area around 42 Orionis (the south-east portion of the reflection nebula), for the entire reflection nebula (including NGC 1973 and NGC 1975), or for the whole nebula complex. This whole region in Orion's Sword was also later catalogued as Orion 1c. In 1966, van den Bergh distinguished the weak clustering of reflection nebulae that includes Sh 2-279 as Ori R2. Every reflection nebula appearing within the Sharpless catalogue was first identified on blue plates of the Palomar Sky Survey, and then double checked against the red plates to eliminate possible plate faults. Van den Berg found that there was a strong concentration of new T Tauri stars around the

, tapering off into a tail approaching Sh 2-279. The Running Man Nebula is a popular target for amateur astrophotographers, as it lies close to the

and has many nearby guide stars. The outline of the running man shows up primarily in photographs; it is difficult to perceive visually through telescopes, though the reflection nebula itself is visible in small to medium apertures in dark skies.

Ionization Source

The whole reflection nebula region is likely excited by the hot young star (YSO) called c Orionis, 42 Orionis or HD 37018 in NGC 1977, which appears as a 4.6 magnitude star some 3.8 from the centre of Sh 2-279. (See image box.) Other massive stars include the yellow giant 45 Orionis and the variable KX Orionis.

Proplyds in NGC 1977

One candidate proplyd was discovered in NGC 1977 with the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

in 2012. The object showed a bent protostellar jet and a possible ionization front facing 42 Orionis, suggesting it is a proplyd. In 2016 a group of astronomers discovered six proplyds with the Hubble Space Telescope and one proplyd with the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicate ...

. The proplyds are pointing to the B-star 42 Orionis, which is the main source of

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

radiation in this region. This ultraviolet light is photoevaporating the proto-planetary disks and the stellar wind of 42 Orionis is shaping the gas into cometary tails. Proplyds were first discovered in large numbers in the

, but there the ultraviolet source responsible for the photoevaporation is the O-type star Theta¹ Orionis C. 42 Orionis is the first instance of a B-type star being responsible for the photoevaporation. All proplyds in NGC 1977 lie within 0.3 parsec of 42 Orionis and two have resolved central sources in the Hubble images, which might be the disks with radii of about 70 and 48

astronomical units The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its mode ...

. NGC 1977 also includes the young star Parengo 2042 (P 2042).

Image gallery

File:Orion Nebula LRGB 2.jpg, Image of the Running Man nebula and its proximity to the Orion nebula. File:NGC1977 CDK Large03.jpg, NGC 1977, Running Man Nebula, by W4SM using 17" PlaneWave CDK, Louisa, VA File:NGC 1977 proplyds zoom.png, Largest proplyd in NGC 1977 seen by Hubble File:Proplyd NGC 1977.png, Proplyd imaged by the Spitzer Space Telescope is the elongated object on the upper left. 42 Orionis is in the middle and it is surrounded by glowing dust.

References

External links

*
Sharpless 279 at Galaxymap

{{NGC20 Orion (constellation) NGC objects Orion molecular cloud complex Reflection nebulae Star-forming regions Sharpless objects