Sharpless 2-3, Gum 58, RCW 120

The Sharpless catalogue is a list of 312  HII regions(emission nebulae), intended to be comprehensive north of declination -27°. (It does include some nebulae south of that declination as well.) The first edition was publishing 1953 with 142 objects (Sh1) and second and final version was published by US astronomer Stewart Sharpless in 1959 with 312 objects

In 1953 Stewart Sharpless joined the staff of the United States Naval Observatory Flagstaff station where he surveyed and cataloged HII regions of the Milky Way Galaxy using the images from the Palomar Sky Survey. From this work Sharpless published his catalog of H II regions in two editions, the first in 1953 with 142 nebula. The second and final edition was published in 1959 with 313 nebulae.

The 312 items in the Sharpless overlap with objects from many other catalogs including the 110 Messier Objects  (M), 7,840 objects in the (NGC), Caldwell Catalogue (which itself is a "best of" from other catalogues, with 109 items), and the RCW Catalogue. Abbreviations for Sharpless objects include, for example using 123, would be Sharpless 123, or Sh2-123, Sh 2-123 (for second one).

Sh2-3 is a reasonably bright example and is about 7.3' x 5.5' in size.