Messier 52: Open Cluster in Cassiopeia

M52 is a compact, rich open cluster in the Milky Way just west of the bright W of Cassiopeia. It is far enough north to be visible all night from mid-northern latitudes, and it is a good target on any clear autumn evening.

What it is

M52 is an open cluster about 5,120 light-years away. Its 13-arcminute size works out to about 19 light-years across. A 1959 study counted 193 probable members within 9 arcminutes of the center. The cluster is young, with an age estimated at about 35 million years. Its brightest stars are two yellow giants; the main-sequence stars are fainter, which gives the cluster its "salt and pepper" look. Dust along our line of sight dims its light and has made its distance hard to pin down. The faint Bubble Nebula (NGC 7635) lies about 35 arcminutes to the southwest.

When to see it

M52 is an autumn object. It is highest around midnight in mid-September and well placed in the evening from September through December. From about 40°N it reaches about 68° in the north and, at declination +61°, it never sets. From the Southern Hemisphere it is low or out of sight; it does not rise at all for observers south of about 28°S.

How to find it

Find the W of Cassiopeia and its two western stars, Schedar (Alpha) and Caph (Beta). Draw a line from Schedar through Caph and keep going about the same distance again, a little over 6° past Caph to the northwest. There you will find the 5th-magnitude star 4 Cassiopeiae. M52 lies about 0.7° south of that star and shows up in a finder as a small hazy patch.

What you will see

In binoculars M52 looks like a small, grainy glow with perhaps one or two stars showing. A small telescope at medium power resolves a few dozen faint stars in a compact group, often described as fan- or V-shaped, with a brighter yellow star at the southwest edge. A larger telescope shows a rich, sparkling cluster of many faint stars against a crowded Milky Way background. In a 200 mm scope under dark skies you can try for the Bubble Nebula nearby; it is faint, and a nebula filter (UHC or O-III) helps.

History

Charles Messier discovered M52 on September 7, 1774, while observing the comet of that year, which passed close to it. Later observers often remarked on its fan-like shape.