Cluster with Nebula NGC 1931
NGC 1931 was discovered by Wilhelm Herschel on 4 February 1793. It is a young star cluster, surrounded by a nebula of gas and dust and has partly amorphous, but partly also a filament-like structure. The dust nebula surrounds a small cluster of faint stars. It resembles a miniature version of the Orion Nebula and is located in a spiral arm of the Milky Way, which is probably an extension of the Perseus arm. Distances vary from 1.8 pkc to 2.16 kpc (5870 to 7050 light years). The nebula has an angular dimension of 4'x4 'and an integrated brightness of 11.3 mag. [196, 219]
As can be seen on the infrared image of the Wide-field Infrared Survey Explorer (WISE) in Fig. 2, NGC 1931 belongs to a larger, loosely connected complex of H-II clouds in the constellation Auriga, to which IC 405, IC 410 (with open star cluster NGC 1893), as well as from the Sharpless catalog Sh 2-231, Sh 2-232, Sh 2-233 and Sh 2-235 belong. However, these are so faint that they cannot be captured visually, but only photographically.
Approximately between the two stars ι Aurigae (Hassaleh) and θ Aurigae is NGC 1931 in the immediate vicinity of the two beautiful open star clusters Messier 36 and Messier 38 and the smaller NGC 1907. About one degree to the west of NGC 1931 is the 5.1 mag bright Star φ Aurigae, which can still be recognized by the eye. This object can be easily observed from September to April.