Cepheus, the King, sits high in the northern sky between Polaris and the W-shaped constellation Cassiopeia. It lies near enough to Polaris that it is circumpolar, never dropping below the horizon at latitudes above 32° N. Cepheus consists of five stars that resemble a child’s drawing of a house. This constellation contains a wide variety of objects—double stars, star clusters, nebulas, and a galaxy or so.
Delta Cephei is one of the better double stars in Cepheus. This star lies around 2.5° east of Zeta Cephei, the star at the bottom left corner of the “house.” With a separation of about 41 arcseconds, Delta Cep is a wide double, easily split at the lowest magnifications. You should even be able to split this double with a binocular. Delta Cep’s component stars have slightly contrasting colors. The primary star is yellow, while the secondary is bluish-white. Besides being a double star, Delta Cep is also a variable star that varies between magnitudes 3.5 and 4.4 over a period of just over 5 days. You can see this variability pretty easily by comparing the brightness of this star with others in the vicinity.
A remarkable star called the Garnet Star lies about 3.5° west-northwest of Zeta Cep. The Garnet Star is both the largest and the reddest star that is easily visible to the unaided eye. If it were placed in the center of our solar system, the outer edge of this star would lie outside the orbit of Jupiter. The Garnet Star is a deeper shade of orange than other bright orange stars like Antares and Betelgeuse, but it is not truly red as are several of the fainter carbon stars.
Struve 2816, perhaps the finest multiple star in Cepheus, lies about 1.5° southwest of the Garnet Star. This star is dim, but visible to the unaided eye from moderately dark skies. Struve 2816 is a triple star, consisting of a yellow primary star moderately separated from two white companion stars. The trio will probably look best at low to moderate magnifications (50–100×). A double star, Struve 2819, lies just east of Struve 2816, near enough that both of the stellar systems are visible in the same field of view.
A very different pair of objects lies in the southwestern corner of Cepheus. NGC 6939, an open star cluster, and NGC 6946, a face-on spiral galaxy, lie just over half a degree apart, 2° southwest of Eta Cephei. Although these two objects are quite different from each other, they both look like round, fuzzy patches of light at low magnifications. Higher magnification will resolve some of the stars in NGC 6939. It is quite a bit harder to coax any detail out of NGC 6946, although experienced observers under dark skies may be able to detect a hint of the galaxy’s spiral structure. Perhaps the most interesting characteristic of this galaxy is the exceptionally high number of supernovas it produces. Ten supernovas appeared within NGC 6946 between 1917 and 2017, giving it the nickname “Fireworks Galaxy.”
NGC 7023, the Iris Nebula, lies about 3.5° southwest of the star Alfirk. The Iris is a complex of reflection and dark nebulosity surrounding a 7th magnitude star, which illuminates the reflection nebulosity. Under dark skies, this nebula is easy to see with a mid-sized telescope at moderate magnification.
The most obvious part of the nebula is the bright area of reflection nebulosity that forms a cloudy halo around the illuminating star. Careful observation should show areas of bright and dark structure within this nebulosity. What I really like about the Iris, though, is the large complex of faint reflection and dark nebulosity that surrounds the bright area of reflection nebulosity. Even under dark skies, you can’t easily see this outer nebulosity. It basically appears as a mostly-starless area that just “feels” cloudy, giving the impression that there is a lot of faint nebulosity just beyond the light grasp of your telescope.
