Deep-Sky Objects in Cassiopeia

M52 and Bubble Nebula
Image Credit: M52 cluster and Bubble Nebula by Lóránd Fényes

Cassiopeia is the 25th largest of the 88 recognized constellations, taking up an area of 598 square degrees of the northern sky. The brightest star in the constellation is Schedar (Alpha Cassiopeiae), a magnitude 2.24 K-type orange giant star that is located about 228 light years away. Note, however, that Schedar is a suspected variable star, whose luminosity varies measurably.

The constellation is visible from latitudes of between +90° and -20°, and being circumpolar can be seen the whole year round from the northern hemisphere. In October, Cassiopeia becomes visible low on north-eastern horizon just after sunset, while November provides the best time to see Cassiopeia, when its distinctive “W” shape is highest in the sky at about 9 PM (Local Time).

Interestingly, Cassiopeia was the constellation in which Tycho Brahe had observed the supernova of 1572 that remained visible to the naked eye for more than a year. Apart from having one associated meteor shower, the Perseid, the constellation contains several interesting, although not spectacular, deep-sky objects, the most notable of which are explored here in this list.

Messier 52 (NGC 7654)

M52Located about 5,000 light years away, M52 has an apparent visual magnitude of 5.0, which makes it a relatively easy target for binocular and small telescopes under dark skies. This cluster is only about 35 million years old, and its two most luminous stars are both yellow giants, with magnitudes of 7.77 and 8.22, respectively. Medium-sized telescopes will clearly show the clusters’ 13 arc-minute diameter that translates into a true diameter of about 19 light years at its distance. Also lying in the direction of Messier 52 is an H II region of space known as the Bubble Nebula (NGC 7635), with this emission nebula illuminated by a its massive, hot, central star called SAO 20575. In an 8 or 10-inch telescope, the the Bubble Nebula appears as a large faint shell surrounding a star.

Messier 103 (NGC 581)

Messier 103Located about 10,000 light years away, M103 is another young open cluster in Cassiopeia, with an estimated age of only 25 million years. All told, M103 contains a total of 172 stars, the brightest of which are B-type stars supergiant and giant stars with an apparent visual magnitude of 10.5. Note, however, that the bright, overexposed stars (the stars shown here with diffraction spikes), are nearby foreground stars. This open cluster is 17.5 light years across and shines with an apparent magnitude of 7.4. It was also the last object to be listed by Charles Messier in his famous catalogue, and appears as a cloudy fan-shaped object using binoculars, while a 4-inch telescopes will resolve its four brightest stars.

Cassiopeia A

Cassiopeia ACassiopeia A is a supernova remnant, and is the not only among the first radio sources to be discovered outside of the solar system, but since its discovery in 1947, it is also the strongest radio source in the entire sky. Although it is not known with certainty what type of star it is that exploded, the cloud of stellar material has an estimated temperature of 50 million degrees F, and is expanding at the rate of between 4,000 and 6 000 km/sec. Most estimates put the remnants’ distance at about 11, 000 light years, and the first light emitted by the supernova is believed to have reached Earth roughly 300 years ago.

The Pacman Nebula (NGC 281)

The Pacman NebulaThe composite X-ray and optical light image shown here shows the H II region in the nebula as a blue streak pointing toward the lower right of the frame. This area represents a bout of recent star forming activity, with the UV light of the young, hot blue stars illuminating the enormous quantity of ionized atomic hydrogen in the larger structure. The nebula is located about 9,500 light years away, and was discovered by E.E. Barnard in 1883, who incidentally, did not give the nebula its current popular name since arcade games had not been invented yet.

The White Rose Cluster (NGC 7789)

The White Rose ClusterCaroline Herschel discovered this pretty cluster in 1783, during a break in her duties as William Herschel’s (her brother) secretary/note taker/assistant. The cluster is also known as Caroline’s Rose or The White Rose, since when seen through a large telescope, the stars in the cluster are arranged in loops and swirls that somewhat resemble the petals of a rose. NGC 7789 is more than 50 light-years wide, and is located about 7,600 light years away. The star cluster is around 1.6 billion years old, with many of its stars red giant, shown in the image oppsite as yellowish in color.

NGC 185

NGC 185Also known as Caldwell 18, NGC 185 is a dwarf spheroidal galaxy, and a satellite galaxy of M31, where it forms a physical pair with NGC 174, another of the Andromeda Galaxy’s satellites. As such, both galaxies are members of the Local Group of Galaxies. Note though that while NGC 85 is an easy target for small telescopes, the low surface brightness of NGC 147 makes it an extremely challenging object to observe with amateur equipment.

Unlike most dwarf elliptical galaxies, NGC 185 is known to contain young star clusters. The galaxy also has an active galactic nucleus, and although this means that it is often classified as a type 2 Seyfert galaxy, its status as a Seyfert galaxy is currently being questioned by many investigators. If it is eventually confirmed as a proper Seyfert galaxy, it will not only be the closest such galaxy to Earth, but the only one in the local Group of galaxies.

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