Cassiopeia Cornucopia — Pretty Little Clusters All in a Row – Sky & Telescope

Open clusters in Cassiopeia
A compact row of star clusters extends for 2.5° starting 2° northwest of Beta (β) Cassiopeiae (Caph). They include objects from the NGC (abbreviated N), Berkeley (Be), Harvard (H), King (K), Teutsch (Teu), Frolov, and Stock (St) catalogs. The faint supernova remnant CTB 1 and emission nebula Sh 2-165 also appear in the vicinity.
DSS2 / Aladin Sky Atlas

I enjoy manually hunting for deep-sky objects no matter where they are in the sky, from star-starved Camelopardalis to easy-peasy Sagittarius with its fistfuls of guide stars. But given the choice, I’ll happily take the path of least resistance. Wouldn’t it be nice to just to point your telescope at a cluster or nebula and effortlessly slide to six or seven more with just the push of a finger? Well, you can.

Pathway to the mini Cassiopeia clusters
Start your open-cluster-hop just off the west end of Cassiopeia, now well placed in the northeastern sky at nightfall. North is up and stars are shown to magnitude 8.
Stellarium with additions by Bob King

Just 2° northwest of Beta (β) Cassiopeiae stretches a remarkable, compact row of eight small open clusters in the space of 2.5°. While not a geometrically perfect line it’s close enough that a simple push takes you from one group to the next. I can easily fit four of these starry splashes in a single 1° field of view. Together they make for a delightful night of observing and a chance to experience the fecundity of the northern Milky Way before winter’s cold bite.

I’ve also included a ninth cluster a short distance off the main trail because it was simply too interesting to pass up. Most of these objects will show well in an 8-inch telescope (and several in smaller instruments) under good skies. I used a 15-inch Dob for my observations. Starting at 2nd-magnitude Caph, I star-hopped to a pair of 6th-magnitude stars, beginning my run at Berkeley 58 and heading northwest. All were visible right off the bat using a magnification of 64×.

Name R.A. Dec. Mag. Dia. # stars
Berkeley 58 00h 00.2m +60° 56.5′ 9.7 5.0′ 39
NGC 7790 23h 58.4m +61° 12.5′ 8.5 5.0′ 134
NGC 7788 23h 56.7m +61° 24.0′ 9.4 4.0′ 20
Frolov 1 23h 57.5m +61° 37.4′ 9.2 ~5.0′ 26
Harvard 21 23h 54.3m +61° 43.7′ 9.0 3.0′ 6
King 12 23h 53.0m +61° 57.0′ 9.0 3.0′ 15
King 21 23h 49.9m +62° 42.0′ 9.6 4.0′ 20
Teutsch 23 23h 47.9m +62° 59.8′ ~9.0 1.8′ ~10
Stock 17 23h 43.8m +62° 09.6′ ~9.5 1.0′ ~15
Information for this table derives from Star Clusters by Brent Archinal and Steven Hynes. Where data was lacking, approximations are my own.

Let’s dive in!

Cluster quad — NGC 7788, 7789, Frolov 1 and Be 58
All four of these treasures fit inside the 1° field of view of my 64× eyepiece. Each cluster has its own character, but NGC 7788 and NGC 7790 are particularly rich and bright.
William Maxwell

Berkeley 58 — A moderately rich cluster of mostly 13th-magnitude and fainter stars with an intriguing, misty appearance. It stands out well despite its weakly concentrated core. The group is elongated northeast-southwest with a shape that reminds me of a bouquet of flowers.

NGC 7790 — Beautiful! A small, rich cluster elongated east-west and sparkling with stars of 10th magnitude and fainter. It stands out boldly in the field of view, with its brightest member — tinged faintly red — at the cluster’s western edge. A loose collection of more luminous stars dominates the cluster’s western half. Fainter, more numerous stars in the eastern half give the object a lopsided appearance. Using averted vision and 142×, I detect short, curved strings of suns within this fainter portion that give it a splashy appearance.

NGC 7788 — A gem you must add to your cluster keepsakes. Despite having a smaller size and lower star count than its neighbor NGC 7790, it’s endowed with a larger number of bright members, and they’re tightly packed together in the form of a lizard’s foot. A 9.2-magnitude star shines close to the cluster’s center. Enjoy at low magnification first, then use moderate power to better appreciate the patterned core.

Beyond the NGC

Milky Way schematic Perseus Arm
This artist’s impression shows the structure of the Milky Way, including the location of the spiral arms and other components such as the central bar. Much of Cassiopeia offers a “window” into the Perseus Arm, the next spiral arm out from our own. Our featured objects are found within the Perseus Arm or between it and the Orion Spur at distances ranging from 6,860 light-years (King 21) to 12,100 light-years (Berkeley 58).
NASA / JPL-Caltech / ESO / R. Hurt

Frolov 1 — A loosely bound group extended north-south. Its brightest members trace a looping figure that resembles a mirror image of the constellation Scorpius. Although star-poor and unconcentrated I can readily distinguish it from random background stars.

Harvard 21 — Sparse and unconcentrated. I see five 12th-magnitude stars arranged in two short arcs along with a smattering of fainter potential cluster members in the vicinity.

King 12 — Gorgeous, compact pile of suns! A tight, equal double star with a separation of ~3″ dominates the cluster’s center. A second fainter, close double lies almost due north of this pair — nice surprises bundled inside a pretty parcel. King 12, along with NGC 7788 and NGC 7790, are all close to each other in the sky and have similar young ages. This suggests that they were all born around the same time within the same giant molecular cloud.

King 21 and Teutsch 23 clusters
Obscure but each oddly compelling, open clusters King 21 and Teutsch 23 are visible in the same low-magnification field of view.
DSS2 / Aladin Sky Atlas

King 21 — Two brighter stars (magnitudes 10.8 and 11.7) stand out in the center of a haze of fainter members that resembles a cloud of tiny gnats. The mist easily resolves at 142× into a pretty, rich halo of similar-magnitude stars extended north-south. The 11.7-magnitude star is a close, unequal pair with a separation of ~4″. A lovely object all in all.

Teutsch 23 — This tiny, compact cluster boasts some 10 suns of magnitude 12 and fainter, two of which are neat doubles when viewed at 150× and higher. Neither bright nor rich, its teeny-weeniness makes it stand out just the same. An 8.4-magnitude star shines just 1.6′ south of the object. Teutsch 23 is a recent addition to the Milky Way’s family, appearing on a list of likely new open clusters in the early 2000s.

Stock 17 swarm
Stock 17 is diminutive ball of stars packed tightly around its brightest member.
PanSTARRS / DR1, Aladin Sky Atlas

Stock 17 — One of 24 open clusters compiled by Jürgen Stock in the early 1950s. I included this out-of-the-way clutch because of its unique appearance. You’ll find it 35′ west of the 5.6-magnitude star 6 Cassiopeiae.

At first you’ll see only its brightest member, an 8.5-magnitude star surrounded by a suspicious, grainy glow. But if you increase the magnification to around 200× and use averted vision, a dense sprinkle of fainter stars materializes, huddled close to the luminary. Several of the stars align to create a pair of “arms” extended in welcome.


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