Angel Nebula (NGC 2170)
History
On 16 October 1784 William Herschel sweeped the sky using his 18.7 inch large reflector and discovered in the constellation Monoceros «a star of the 9th magnitude with a milky chevelure irregularly elliptical» which he cataloged as IV 19. [463] His son John later cataloged the nebula as GC 1362 and noted: «Star of 9th magnitude in very faint, pretty large nebula, extended towards 170°» [467] In 1888 John L. E. Dreyer listed the nebula as NGC 2170 in his «New General Catalogue». [313]
In 1946 Sven Cederblad published a study of bright diffuse galactic nebulae where he listed NGC 2170 as Cederblad 63. [130]
In 1965 Beverly T. Lynds published a catalogue of bright nebulae from a study of the red and blue prints of the Palomar Observatory Sky Atlas. The nebula is there referred as LBN 213.69-12.65 (or also just LBN 994). [270]
Just one year later in 1966 Sydney van den Bergh published his study of stars surrounded by reflection nebulae, also based on the red and blue prints of the Palomar Observatory Sky Atlas. He identified the following four nebulae: vdB 67, 68, 69 and 72. For vdB 67 he was uncertain. [264]
Physical Properties
The reflection nebulae belong to the Monoceros R2 Molecular Cloud, which contains a cluster that is one of the closest massive star forming regions that is still embedded in its natal molecular cloud. The cluster contains several hundred stars which are obscured by dark clouds. The three brightest infrared sources in the Mon R2 region are IRS 1, IRS 2, and IRS 3. IRS 1 is the ionizing source of a compact HII region. IRS 2 illuminates the prominent ring nebulosity in the central part of the star forming region. IRS 3 is the brightest infrared source and probably the most luminous young stellar object in the cloud. It is optically invisible and has no associated HII region. This probably reflects the very early evolutionary stage of IRS 3, which apparently has not yet developed an HII region. [131]
| Designation | NGC 2170 |
| Type | RN |
| Right Ascension (J2000.0) | 06h 07m 31.3s |
| Declination (J2000.0) | -06° 23' 53" |
| Diameter | 2 × 2 arcmin |
| Metric Distance | 0.740 kpc |
| Dreyer Description | * 9 in vF, pL neb, E 170° |
| Identification, Remarks | WH IV 19; GC 1362; LBN 994 |
Finder Chart
The reflection nebula NGC 2170 is located in the constellation Monoceros. The best season for observation is from October until March.
