| Emission nebula | |
|---|---|
| H II region | |
As seen by theDESI Legacy Survey | |
| Observation data:epoch | |
| Right ascension | 17h 19m 48.5s |
| Declination | −39° 20′ 19″[1] |
| Distance | 8,800 ly (2,700 pc) |
| Apparent magnitude (V) | 14.95[2] |
| Apparent dimensions (V) | 5' |
| Constellation | Scorpius |
| Designations | RCW 121, ESO 333-3,IRAS 17149-3916,Haro 3-6, PN H 2-6[3] |
| See also:Lists of nebulae | |
Sh 2-4 is anemission nebula in the constellationScorpius. It is part of theSharpless Catalog assembled byStewart Sharpless.[4] It was originally misidentified as aplanetary nebula. The incorrect planetary designation PN H 2-6 can still be used as an identifier. It may be associated with the star cluster Havlen-Moffat 1.[1]
The nebula is bright, and visible with longer exposure. The nebula mostly emits red light, making viewing through ahydrogen-alpha filter effective.[5]
Havlen-Moffat 1 is known to be a source of ionization within Sh 2-4. The nebula contains twoWolf-Rayet stars, designated WR 87 and WR 89.[6] Contained within the nebula is the infrared cluster [DBS2003] 118.[7]
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