NGC 2158 is a rich, compact open cluster in Gemini that presents a dense, almost globular-like knot of faint stars to the astrophotographer’s camera. Spanning only 5.3′ across the sky, it rewards long focal lengths and steady seeing to resolve its tightly packed members. Its considerable distance of about 27,600 light-years means the individual stars appear dim, so patient integration and clean tracking pay off in bringing out its subtle stellar swarm. Because it sits close to the far brighter and looser open cluster Messier 35, NGC 2158 is often captured as a striking contrasting companion in wide-field frames.
Names and Catalog numbers
- NGC 2158
- Mel 40 (Melotte 40)
Position and the cosmic neighborhood
Located in Gemini at a right ascension of 06 07 26.90 and a declination of +24 05 56.0, NGC 2158 lies in a region well placed for northern-hemisphere imagers during the winter months. Its most photogenic neighbor is the sprawling open cluster Messier 35, which sits nearby in the same field and makes an ideal anchor for wide-angle compositions. Framing both clusters together highlights the dramatic contrast between the loose, bright stars of Messier 35 and the tight, distant grain of NGC 2158, offering a compelling depth cue within a single exposure.
Nice to Know
- NGC 2158 is one of the most rewarding photographic companions to Messier 35, appearing as a compact stellar knot beside its larger neighbor.
- At roughly 27,600 light-years away, it is a distant cluster whose faint members demand long integration times to record well.
- With an apparent size of just 5.3′, its tightly concentrated form often causes it to be mistaken for a globular cluster in images.
- It carries the additional catalog designation Mel 40, cataloged by Melotte alongside its NGC entry.
Brightness, distance and size
It lies about 27,600 light-years from Earth and spans roughly 43 light-years across. On the sky it appears about 5.3′ in size.
