Cassiopeia (pronounced kass ee oh pee’ uh) the Queen is one of the first constellations amateur astronomers come to recognize. That’s because its five brightest stars form an asterism that looks like a large letter W.
Cassiopeia is observable in the autumn and winter throughout the Northern Hemisphere. It lies opposite the Sun in early October. And if your location on Earth is at 46° north latitude or higher, this constellation is circumpolar, meaning that it will never set.
Among the 88 official constellations, Cassiopeia ranks as the 25th largest and 30th brightest. It contains four stars (Alpha [α], Beta [β], Gamma [γ], and Delta [δ] Cassiopeiae) that are among the top 200 brightest in the sky.
From the west to the east
The first target on our list is both famous and difficult to see well: the Bubble Nebula (NGC 7635). It’s also the 11th object on Sir Patrick Moore’s Caldwell list and No. 162 on Stewart Sharpless’ list of emission nebulae. The easiest way to find it (without a go-to drive) is to first find the next object on this list, M52, and look a bit more than ½° to the southeast.
The Bubble measures 15′ by 8′ in angular size and is a favorite target for astroimagers. Through an 8-inch telescope, however, you’ll see just a faint arc that measures 3′ by 1′, surrounding a 9th-magnitude star designated BD+60°2522. This star is more than 40 times the mass of our Sun and emits an intense stellar wind. The outer boundaries of the Bubble are where the edge of the wind is interacting with the surrounding nebulosity.
The Bubble isn’t a perfect sphere, of course, because the gas it’s expanding into isn’t uniform. In some places it’s more dense than others. The thickest gas lies to the northeast, which slows the Bubble’s expansion in that direction.
The result is that the Bubble isn’t perfectly centered on BD+60°2522.
A large telescope — 16 inches or larger — is the way to view this object. Through such an instrument, you’ll see the entire sphere. Also use a nebula filter, because it will dim the many faint background stars.
The second object on our list is open cluster M52 (NGC 7654). It glows at magnitude 7.3 and has a diameter of 13′. To find it, begin by drawing a line from Schedar (Alpha [α] Cas) to Caph (Beta [β] Cas) — these stars are 5° apart. Extend the line another 6°, and you’ll land on M52.
As with most open clusters on Messier’s list, the individual stars are relatively bright and stand out well. In M52, they lie in the 8th- through 12th-magnitude range. An 8-inch scope on a night of good seeing will reveal some 75 members.
Next up is open cluster NGC 7789. Because it’s so attractive, it has two common names. The first is the Crab Cluster, due to the way famed British observer Admiral William Henry Smyth described it in his 1844 Cycle of Celestial Objects: For the Use of Naval, Military, and Private Astronomers. In fact, it is the last object he describes in that two-volume set (probably because its right ascension is 23h57m). Smyth wrote, “It is, indeed, a very glorious assemblage, both in extent and richness, having spangly rays of stars which give it a remote resemblance to a crab, the claws reaching the confines of the space in view.”
The second common name, Herschel’s Spiral Cluster, comes from the facts that British astronomer Caroline Herschel discovered it in 1783, and that some of the stars in the cluster form a counterclockwise spiral.
You’ll find it midway between Sigma (σ) and Rho (ρ) Cas. It glows at magnitude 6.7 and spans 16′. Use a 4-inch telescope with a magnification around 100x, and you’ll be able to count up to 50 stars. Move up to an 8-inch scope and that number will double.
The first trough
The first double star on our list is Sigma (σ) Cassiopeiae. Its components are modest, with magnitudes of 5.0 and 7.2, so an easy way to find it is to look a bit more than 3½° south-southwest of Caph.
The two stars are separated by just 3″, so use an eyepiece that will give you a magnification around 150x to split them. Most observers see both stars as white; some see a tinge of blue in them. Human eyes can vary significantly, so the colors you see may be different.
Believe it or not, Cassiopeia does contain galaxies, and our next object is proof. It’s irregular galaxy IC 10, which you can find by looking 1½° east of Caph.
If you knew nothing about IC 10 and I told you it was 2.2 million light-years away (slightly less than the distance of the Andromeda Galaxy [M31]), you’d probably think, “This has to be a celestial showpiece!” But that’s not the case. First, it’s only 5,000 light-years across — much smaller than M31 — and second, it’s in the Milky Way’s plane, so plenty of dust and gas lie within our line of sight.
IC 10 has a magnitude of 10.3 and a size that measures about 7′ by 6′. Your best bet to observe it is to point at least an 11-inch scope with a low-power eyepiece in its direction and pan around until you see a gradual brightening of the background. Level up to a 16-inch and you’ll start spotting some of the star-forming regions in the galaxy’s plane.
The next object is open cluster NGC 129, which, at magnitude 6.5, lies right at the edge of naked-eye visibility. You’ll find it midway between Caph and a star unofficially named Tsih (Gamma Cas). It’s not a small object, sporting a diameter of 21′.
Within that area, an 8-inch scope with an eyepiece yielding 100x will reveal some 25 stars evenly spread out; an 11-inch scope will double that number.
The second galaxy on our list, this time a dwarf elliptical, is NGC 147, also known as Caldwell 17. And although it lies within the boundaries of Cassiopeia, it’s actually one of the Andromeda Galaxy’s satellites. You’ll find it roughly 2° west of Omicron (ο) Cas, although spotting it is a bit of a challenge.
NGC 147 glows at magnitude 9.5 — worthy for a galaxy — but that brightness is spread over an area measuring 15′ by 9.4′. When scanning the area, do so carefully and look for an oval halo that’s a bit brighter than the background glow.
In contrast to faint NGC 147, next up is the impressive Sailboat Cluster (NGC 225). To see it, point your scope roughly 2° northwest of Tsih. It glows at magnitude 7.0 and spans 12′, half the diameter of the Full Moon. The cluster divides nicely into two starry regions, one a bit fainter than the other.
Astronomy contributor Rod Pommier gave this object its common name because of its four-star arc that, to him, outlines the leading edge of a sail. A mast of four stars in a line supports the sail. That line connects to a boat outlined by eight stars.
Achird (Eta [η] Cassiopeiae) is the second double star on our list, and it’s a nice one. The primary glows at magnitude 3.4 and the secondary at magnitude 7.5. The two stars are separated by 11″.
If you have trouble locating it, just look 1.7° northeast of Schedar. Low power works best to show the brighter star as yellow and its partner as red. High magnifications accentuate their brightness and make them look white and yellow.
Next up is the Pacman Nebula (NGC 281). You’ll find it 1¾° east of Schedar. It measures a worthy 35′ by 30′, making its area nearly 20 percent larger than that of the Full Moon.
Following the 1980 release of the Namco video game Pac-Man, imagers noticed the nebula’s resemblance to the titular character. If you use an 11-inch or larger scope, you will, too. Insert a nebula filter and look for the dark lane that divides the brighter from the dimmer portion. A 7th-magnitude star (Pacman’s eye) shines through the brightest part of the nebula.
What’s left of the crown
When you’re done with the Pacman Nebula, it’s time to observe the Owl Cluster (NGC 457). To find it, point your scope 2° south of Ruchbah (Delta Cass). It glows at magnitude 6.4 and has a diameter of 13′.
While observing this cluster in 1977, Astronomy magazine Editor David J. Eicher saw an owl figure in the cluster’s overall shape, whose eyes were the two brightest stars. He dubbed it the Owl Cluster, and it’s carried that name ever since.
NGC 457 is loaded with stars. An 8-inch scope at low power will reveal nearly 100. Its most luminous star, within the cluster, shines at magnitude 8.6. In addition to the cluster, note the uniform background glow caused by distant, unresolved Milky Way stars.
Next up is the second (and last) Messier object in the constellation, open cluster M103 (NGC 581). To find it, look 1° east-northeast of Ruchbah. It glows at magnitude 7.4 and spans 6′.
M103 contains three dozen stars with magnitudes between 8 and 13, and together they stand out well from the Milky Way. Most observers see the majority of stars forming a tight triangle. Use a magnification around 100x.
Sometimes, objects appear brighter than their listed magnitudes. That’s the case with open cluster NGC 663, also known as Caldwell 10. Catalogs show it at magnitude 7.1, but I and other observers have seen it naked-eye from dark sites.
To find this object, first locate the magnitude 5.8 star 44 Cas. Then move ¾° north-northeast. Along the way, you’ll pass the 8th-magnitude cluster NGC 659, which I promise you won’t see naked-eye.
NGC 663 has a diameter of 16′. If you view it through a 4- to 8-inch scope at a magnification around 75x, you’ll see two faint stellar chains, each containing about 20 stars, with a dark space between them. Each chain ends at a pair of brighter stars. View the cluster through an 11-inch scope, though, and the dark space disappears. The star count then approaches 100.
Next, take a look at an object from a different catalog. German astronomer Jürgen Stock compiled a list of 24 open clusters in the 1950s. This one, Stock 2, glows at magnitude 4.4 and spans a full degree.
To find it, look a bit north of the midway point between Ruchbah and Eta Persei. Although you can see it naked-eye or through binoculars, the best views are through telescopes with eyepieces that keep the magnification below 50x. You’ll see a loose collection of some 50 stars in the 8th- to 10th-magnitude range.
In the minds of most observers — and especially imagers — the next two objects go together as a pair. They are the Heart and Soul nebulae (IC 1805 and Westerhout 5, respectively). To further complicate things, the brightest part of IC 1805 — a nebulous clump to the northwest — carries its own designation, NGC 896, because it was discovered before the rest of the nebula. Indeed, you’ll probably spot it first, too. Also, the energy lighting up the Heart comes from the small open cluster Melotte 15 at its center. And finally, while you’ll see lots of references that state the
Soul Nebula is IC 1848, that designation belongs to an open cluster within the nebula.
Both of these objects each span 1°, but because the Soul doesn’t cover as much area, it appears more condensed. To find the Heart, look 5° east-southeast of Segin (Epsilon [ε] Cas). Once you find it, look another 2½° east-southeast for the Soul.
Because of their size, you can approach observing these objects either with low or high magnification. You will, however, need to use an 8-inch or larger scope from a dark site plus a nebula filter.
For an overall look at the Heart, use an eyepiece that gives about a 1° field of view. Start by identifying the brightest areas: NGC 896, Melotte 15, and the slightly brighter crescent of gas on the western edge.
When you move to the Soul Nebula, you’ll immediately see why it’s often also called the Baby Nebula. Two large nebulous areas make up the head and body. The head looks denser and contains three faint open clusters cataloged by Swedish astronomer Per Collinder. The body has the star cluster IC 1848 inside. You’ll see those stars better if you remove the nebula filter.
As you can see by this list, the Queen contains many objects worthy of a look — a long, highly magnified look.
