How to Find and Observe M52, an Open Cluster

The northern constellation of Cassiopeia contains so many showpiece clusters it’s a wonder Messier only included two of them in his catalog.

Fortunately, M52, the first of those two open clusters, is a rich and rewarding object for telescopes of all sizes. In this article, I’ll show you how to find this highlight of the autumn sky, and what you can expect to see when you have M52 in your eyepiece.

M52 Vital Statistics

When Was M52 Discovered and What Do We Know About it?

M52 was discovered in September 1774 by Charles Messier, who described it as a “cluster of very small stars, mingled with nebulosity.”

Typical of open clusters, M52 is young; some estimates give it an age of just 25 million years, although it may have experienced two consecutive episodes of star formation.

It is also one of the very richest open clusters in the Messier catalog, with a star density near the center of 1.5 stars per cubic light-year (although that is nowhere near as dense as M15). The cluster itself is 22 light-years across.

M52 also contains a respectable number of variable stars (including 18 pulsating variables), providing an ideal opportunity for researchers to monitor multiple targets in the same field of view.

When is M52 Visible?

This table shows when you can best see M52 from the mid-latitudes of the northern hemisphere. Times given are approximate local times for mid-month using a 24hr clock. Underlined times are during the hours of darkness.

If you’ve read previous articles in this series, you may be wondering why there are no Rise or Set times.

This is because M52 is circumpolar for many northern hemisphere observers, meaning that it never sets, so can be observed all year round and all night long. It’s the third most northerly Messier object, after the galaxy pair M81 and M82.

That said, M52 is best observed during the months of September through to December if you want to see it at its highest elevation.

Difficulty

From my suburban location (on the threshold between Bortle 5 and 6), M52 is visible in 7×50 binoculars as a misty, grainy patch of light. Observers peering through urban skies might struggle to see it in binoculars and finders, but it remains a fine telescopic object. 

How to Find M52

Popular atlas references:

• Sky & Telescope’s Pocket Sky Atlas: charts 71 and 72
• Sky Atlas 2000: chart 3

M52 lies within the circumpolar constellation of Cassiopeia, the Queen. The Milky Way passes through here and the region is especially rich in open clusters.

The following star charts, from SkySafari 6, will show you how to locate M52. Each chart can be clicked on for a full-screen version.

The distinctive W-shaped (or M-shaped) outline of Cassiopeia should be obvious to most observers, but if you’re new to astronomy, the easiest way to find it is to remember that it’s on the opposite side of the Pole Star to Ursa Major (the Great Bear).

When Ursa Major is low, Cassiopeia is high, and vice versa. The first star chart shows M52, in green, at 9pm in the middle of October. Note how high towards the zenith (overhead) it is.

Stars are shown to magnitude 5.0, and we’ve marked the route from Ursa Major (Big Dipper/Plough), to the Pole Star (Polaris, in Ursa Minor) and on to Cassiopeia using orange arrows.

To find M52 extend a line through Schedar and Caph (Alpha and Beta Cassiopeiae, respectively), that are on the western, or right-hand side of Cassiopeia’s ‘W’.

Continue this line on for roughly the same distance until you reach the 5th magnitude star 4 Cassiopeiae (which has a distinctive reddish hue).

The details can be seen in the star map below.

This final zoomed-in image shows stars to magnitude 8.0. M52 is at the center of red Telrad finderscope circles. The outer blue circle is a 5° field of view which is typical of a magnifying finderscope.

Through my 9×50 finder M52 appears as a fan-shaped patch of light with a single 8th magnitude star at its apex. If you can’t see it in your finder, aim slightly south of 4 Cassiopeiae and it should be visible in your telescope’s field of view.

M52 through a Telescope

Small Telescopes

M52 is an attractive sight in small telescopes when viewed at low-to-medium powers.

My 4-inch refractor (at 45x) showed it as a rich mass of faint stars with a bright star at the southwest corner. This star was once thought to be an interloper, but recent research indicates it most likely is a true member of the cluster. It is thought to be a giant star burning through its nuclear fuel at a faster rate than its less massive siblings.

Medium-to-large Telescopes

M52 is a magnificent sight in larger telescopes, particularly when viewed in wide-field eyepieces that can show it in the context of the surrounding Milky Way.

In my 10-inch reflector at 133x, it appears as a rich, delta-shaped cluster in a busy star-field. This shape tends to be drowned out in photographs but it’s quite distinctive through the eyepiece. 

Renowned observer Stephen J. O’Meara extends the shape into the surrounding star-field to see a pattern resembling a scorpion, whereas 19th Century observer Admiral William Henry Smyth saw it as “a bird with outspread wings”. What do you see when you look at M52?

M52’s member stars have a range of several magnitudes but they are all outshone by the bright 8.3 magnitude star at the apex of the delta, on the southwest corner of the cluster. Some observing guides seem to overstate the redness of this star; I personally see it as having a more subtle pale yellow-orange hue, and not nearly as red as 4 Cassiopeiae to the north.

Another feature in M52 that I find quite prominent through the eyepiece is an elongated clump of stars on the northeast side of the cluster (the back of the delta).

Beyond M52

When you’ve finished looking at M52, nudge your telescope half a degree southwest and see if you can spot the elusive Bubble Nebula (NGC 7635), discovered by William Herschel in 1787. (If you’re not sure of the correct orientation, the delta shape of M52 points towards it.)

This faint emission nebula is the subject of one of my all-time favorite Hubble images, but it’s easy to overlook in an amateur telescope.

At best I can just make out (using averted vision) a diaphanous crescent-shaped patch of nebulosity, like one half of a Chinese Yin and Yang symbol. Narrowband and OIII filters can help dim the glare from the central 8.5 magnitude star, but otherwise, the improvement is subtle.

M52 and NGC 7635 lie close to the boundary between Cassiopeia and Cepheus, and deep-sky guides that group their subjects by constellation often do this part of the sky a disservice, as many observers might be unaware that an enticing array of clusters and nebulae lie a gentle nudge of the telescope west, just across the border in Cepheus.

These include the compact and curiously fang-shaped open cluster NGC 7510, and its neighbor Markarian 50 which, despite its obscure designation, stands out from the surrounding star-fields as a tiny, crescent-shaped cluster.

The nearby nebulae NGC 7538 (nicknamed the Northern Lagoon for its photographic appearance) and IC 1470 are also worth tracking down, although the former requires a narrowband or OIII filter to be seen well. The latter (IC 1470) is small but relatively bright and is best seen at powers of 150x and above.

All of these objects are plotted on the star map below. It shows stars to magnitude 8.0 and can be clicked on for a full-screen version.

Finally, as if the area around M52 wasn’t crowded enough, it would be remiss of me not to mention Nova Cassiopeia 2021 (V1405 Cas), which flared into prominence in March of 2021. It forms a right-angled triangle with M52 and the Bubble Nebula, lying just south of the former.

Since its discovery by Japanese amateur Yuji Nakamura, it has risen and fallen in brightness; in May it climbed as high as magnitude 5.7. At the time of writing (early September 2021) it was creeping back up in brightness again to somewhere around magnitude 7.

Between this, the now-you-see-it-now-you-don’t V1674 Herculis, and the dramatic re-emergence of RS Ophiuchi, 2021 has been quite the year for bright novae.

Summary

If you haven’t seen M52 before, hopefully, this article has inspired you to seek out this superb cluster and its diverse collection of neighbors.

Just don’t make any plans to get up early the next morning, as you could easily spend several hours exploring this wonderfully rich corner of the Milky Way.

Links / Other Info

• The Bubble and M52 | Astronomy Picture of the Day
• M52 – Deep Sky Videos (Brady Haran)