Sh 2-4
Sh 2-4 is an emission nebula in the constellation Scorpius. It is part of the Sharpless Catalog assembled by Stewart Sharpless. It was originally misidentified as a planetary 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.
Visibility
The nebula is bright, and visible with longer exposure. The nebula mostly emits red light, making viewing through a hydrogen-alpha filter effective.Structure
Havlen-Moffat 1 is known to be a source of ionization within Sh 2-4. The nebula contains two Wolf-Rayet stars, designated WR 87 and WR 89. Contained within the nebula is the infrared cluster118.