Caldwell 54 — Open Cluster in Monoceros
NGC 2506
About C54
Description
NGC 2506 is an open cluster in Monoceros, about 10,000 light-years away. It is a rich, compact cluster containing over 150 stars concentrated in about 7 arcminutes, with an age of roughly 2 billion years.
Observing Tips
Visible as a hazy, unresolved patch in a 4-inch telescope. An 8-inch scope begins to resolve the brighter stars at 100x+. The cluster's distance makes it harder to resolve than most open clusters. Best in winter evenings.
History
Discovered by William Herschel on February 23, 1791. Its great distance and old age make it a valuable laboratory for studying stellar evolution in open clusters.
Fun Facts
At about 2 billion years old, NGC 2506 is one of the oldest open clusters still recognizable as a cluster. It has survived because it orbits relatively far from the galactic plane, avoiding the gravitational disruptions that tear most clusters apart.
Observe
1Properties
Position & Identifiers
2How easy to spot?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Easy | Easy | Easy |
| 150 mm Newton 150mm Newt. | Easy | Easy | Easy |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
3Visibility
Set a location in User Settings to see visibility data.
4
Eyepiece View
5
Best Magnification
6Where this cluster sits in time
Open clusters span more than four orders of magnitude in age — from newborn OB associations to ancient, metal-rich survivors.
7
Colour-Magnitude Diagram
A cluster's colour-magnitude diagram reveals its age: the bluer the turn-off point where the main sequence bends into red giants, the younger the cluster.
Each point is a Gaia-DR3 member. Colour encodes spectral type; size reflects membership probability.
Explore
8
Classification Decoder
Discover
9
Light Travel Time Machine
10
Relativistic Travel
Community Photos (1)
Credit: YayLol123. License: CC BY 4.0. (Wikimedia Commons)
Skybred Mar 2, 2026
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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