Messier 50 (NGC 2323): That’s an “M” for Monoceros! An Open Star Cluster in Monoceros

Messier 50 is an open star cluster in the constellation Monoceros. It’s best viewed in winter.

Discovered by Giovanni Domenico Cassini in 1710, Messier 50 is part of the constellation Monoceros but lies near Canis Major. I’ve read various descriptions of the cluster over the years, including it looking like a “coil,” a “heart,” or, in my case, the letter M. It is bright enough to view in binoculars from suburban skies, while telescopes will bring out fainter stars and greater detail.

One interesting feature of M50 is the presence of several variable stars within the cluster. These stars are known as cepheids, and they pulsate in a regular pattern, changing in brightness over a period of several days or weeks. By observing these variable stars, astronomers can determine the distance to the cluster with great accuracy.

My Observations

This cluster was not as brilliant in the eyepiece as I hoped. Based on images and sketches I’ve seen online, I was expecting M50 to be more robust. Instead, the cluster doesn’t appear as dense as I thought it would. Perhaps it has around 200 stars? It does make an interesting “M” or heart shape in the middle.

Key Stats

Historical Observations

April 5, 1772, observation by Charles Messier

“Cluster of small stars, more or less brilliant, above the right loins of the Unicorn, above the star Theta of the ear of Canis Major, & near a star of 7th magnitude. It was while observing the Comet of 1772 that M. Messier observed this cluster. He has reported it on the chart of that comet, on which its trace has been drawn. Mem. Acad. 1772.”

Sources and Notes

Photo of M50 by Ole Nielson and licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license.

Charles Messier Observations: SEDS Messier Database