Messier 50 — Open Cluster in Monoceros

M50 is a moderately rich open star cluster in the constellation Monoceros, located about 3,200 light-years from Earth. It contains roughly 200 stars packed into a sphere about 20 light-years across. At magnitude 5.9, it is just at the limit of naked-eye visibility under excellent conditions. The cluster has an apparent diameter of about 16 arcminutes. M50 is estimated to be about 78-130 million years old. A distinctive red giant star (spectral type M) sits near the southern edge of the cluster, providing a striking color contrast against the predominantly blue-white young stars.

Located about 9 degrees due north of Sirius, roughly one-third of the way from Sirius to Procyon. Binoculars show a moderately condensed, hazy knot of faint stars. A 4-inch telescope at 60-100x resolves the cluster nicely, showing a heart-shaped or wedge-shaped concentration of stars with a brighter core region. Look for the reddish star near the southern edge — it stands out prominently against the blue-white cluster members. An 8-inch telescope reveals a beautiful, rich field of stars. Best observed from December through March.

Discovered by Giovanni Domenico Cassini around 1711 and independently found by Charles Messier in 1772, who described it as 'a cluster of faint stars near the unicorn, mixed with nebulosity.' The 'nebulosity' Messier noted was simply the unresolved light of the fainter cluster members. The cluster was included in the NGC catalog as NGC 2323.