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M48 is a large conspicuous open cluster covering almost a degree of sky in the constellation of Hydra. It's located close to the border with Monoceros. At magnitude +5.5, the cluster is visible to the naked eye under reasonably dark skies, and a superb binocular or small telescope object. It's best seen during the months of December, January and February.

Charles Messier discovered and cataloged M48 on February 19, 1771. However, he made a positioning mistake and hence the object was missing for over 150 years, until it was identified by Oswald Thomas in 1934, and independently by T.F. Morris in 1959. Since M48 was lost, two subsequent independent re-discoveries occurred. The first was by Johann Elert Bode who found it before 1782 and then Caroline Herschel located it on March 8, 1783.

Hydra is the largest constellation in the sky, but finding M48 is relatively easy as it's positioned just 14 degrees southeast of Procyon (α CMi) in Canis Minor. At magnitude +0.34, Procyon is the seventh brightest star in the night sky. Also visible to the naked eye, but better seen with binoculars is a triangle of 4th and 5th magnitude stars located about 5 degrees northwest of M48. The stars in question are Zeta Mon (ζ Mon - mag. +4.4), 28 Mon (mag. + 4.7) and 27 Mon (mag. +4.9).

M48 Open Cluster (credit:- NOAO/AURA/NSF)

Finder Chart for M48 (credit:- freestarcharts)

Finder Chart for M48 - pdf format (credit:- freestarcharts)

M48 appears as a large faint misty patch of light to the naked eye. Through 7x50 or 10x50 binoculars, it looks somewhat like a fainter and smaller version of the Praesepe (M44). With a small 80mm (3.1-inch) scope, the cluster appears superb with many stars visible arranged in a triangle shape. The stars are concentrated more towards the centre part of the cluster, which in total spans 54 arc minutes of apparent sky. The brightest members are of 8th magnitude. Since it covers nearly twice the size of the full Moon, M48 is best viewed at low magnifications. Telescopes of 150mm (6-inch) aperture reveal about 50 stars brighter than 13th magnitude, with the total number of stars estimated to be about 80.

M48 is 1,500 light-years distant, which corresponds to a spatial diameter of 24 light-years. It's estimated to be 300 million years old.

M48 Data Table

Object TypeOpen cluster
Distance (light-years)1,500
Apparent Mag.+5.5
RA (J2000)08h 13m 43s
DEC (J2000)-05d 45m 02s
Apparent Size (arc mins)54 x 54
Radius (light-years)12
Age (years)300 Million
Number of Stars80
Other NameCollinder 179