Coma Berenices is a traditional asterism that has since become a constellation. It is located near Leo, and was originally considered to be the tuft of hair on the end of Leo's tail.

Notable features

Coma Berenices contains the North Galactic Pole, at right ascension and declination (epoch J2000.0).

The constellation is not particularly bright, having no stars brighter than fourth magnitude. β Comae Berenices is the brightest star in the constellation, at magnitude 4.26. It is intrinsically only slightly brighter than the Sun, which gives us an idea of how faint the Sun would appear seen from 27 light years away.

The second brightest star in Coma Berenices is α Comae Berenices (4.32^m), also called Diadem. The name represents the gem in Berenice's crown. It is a binary star, with two components of almost equal magnitude. Because the orbital plane is so close to the Earth's line of sight, it was long suspected of being an eclipsing binary, but it now appears that the orbital tilt is 0.1° relative to the line of sight, so the stars do not eclipse each other as seen from Earth.

The only other fourth magnitude star in Coma Berenices is γ Comae Berenices (4.36^m).

Over 200 variable stars are known in Coma Berenices, although many of them are obscure. FK Comae Berenices, which varies between 8.14^m and 8.33^m over a period of 2.4 days, is the prototype for the FK Com class of variable stars. It is believed that the variability of FK Com stars is caused by large, cool spots on the rotating surfaces of the stars. FS Comae Berenices is a semiregular variable that varies between 5.3^m and 6.1^m over a period of 58 days. R Comae Berenices is a Mira variable star that varies between 7.1^m and 14.6^m over a period of 363 days.

Notable deep sky objects

Although Coma Berenices is not a large constellation, it contains eight Messier objects. The constellation is rich in galaxies, containing the northern part of the Virgo cluster. There are also several globular clusters to be seen. These objects can be seen with minimal obscuration from dust because the constellation is not in the direction of the galactic plane. However, because of this fact, there are few open clusters (except for the Coma Berenices Cluster, which dominates the northern part of the constellation), diffuse nebulae, or planetary nebulae.

Coma Berenices Cluster

The Coma Berenices Cluster does not have a Messier or an NGC designation, but it is in the Melotte catalogue of open clusters, where it is designated Melotte 111. It is a large, diffuse open cluster of stars that range between 5th and 10th magnitudes, including several of the naked eye stars in the constellation. The cluster is spread over a huge region, more than 5 degrees across, near γ Coma Berenices. The cluster has such a large apparent size because it is relatively nearby, only around 270 light years away.

Named Stars

Richard Hinckley Allen lists among others the following star names for stars in Coma:

Bayer	Name	Origin	Meaning
α Com	Diadem	Latin	diadem
β Com	Al Ḍafīrah	Arabic	the curl
ρ Com	Shang Tseang	Chinese	higher army general
21 Com	Kissīn	Greek???	species of ivy

Galaxies

A large number of galaxies are visible in Coma Berenices, including seven Messier objects.

Virgo cluster of galaxies

Coma Berenices contains the northern portion of the Virgo cluster (also known as the Coma-Virgo cluster), which is around 60 million light years away.

M100 (NGC 4321) is a 9.4^m spiral galaxy seen face-on. At 7 arcminutes across, it has the largest apparent size of any galaxy in the Virgo cluster. It is located about 56 million light-years away. Its diameter is over 120,000 light years, making it among the largest spiral galaxies in the Virgo cluster. Photographs reveal a brilliant core, two prominent spiral arms and an array of secondary ones, as well as several dust lanes.

M85 (NGC 4382) is a lenticular galaxy that is the northernmost outlier of the Virgo cluster. It is one of the brighter members of the cluster. M98 (NGC 4192) is a bright, elongated spiral that is seen nearly edge-on. It has a small nucleus and faint but vast spiral arms. M99 (NGC 4254), about 1.5° southeast of M98, is a bright, round spiral seen face-on. R.H. Allen called it the "Pinwheel nebula", although this name is more often applied to the Triangulum Galaxy.

M88 (NGC 4501) is a multi-arm spiral galaxy, seen about 30° from edge-on.

M91 (NGC 4548) is a barred spiral galaxy.

Coma cluster of galaxies

The Coma cluster of galaxies is to the north of the Virgo cluster. It lies much further away, however, around 230 to 300 million light years away. The cluster is quite large, containing 1,000 large galaxies and possibly up to 30,000 smaller ones. A survey by Fritz Zwicky in 1957 identified 29,951 galaxies in the area that are brighter than 19.0^m. While some of these may be distant background objects, the total number of galaxies in the cluster is quite large.

Due to the great distance to the cluster, most of the galaxies are only visible in large telescopes. The brightest members are NGC 4889 and NGC 4874, both of which are of thirteenth magnitude, with most of the other members being of fifteenth magnitude or dimmer. NGC 4889 is a giant elliptical galaxy.

Other galaxies

M64 (NGC 4826) is known as the Black Eye Galaxy because of its prominent dark dust lane in front of the galaxy's bright nucleus. It is relatively nearby, at around 17 million light years away from Earth. Recent studies have revealed that the interstellar gas in the outer regions of the galaxy rotates in the opposite direction from that in the inner regions, leading astronomers to believe that at least one satellite galaxy had collided with it less than a billion years ago.

NGC 4565 is a spiral galaxy that is seen edge-on, and is called the "Needle Galaxy" for that reason. With an apparent length of 16 arcminutes, it has the largest apparent size of any galaxy seen edgewise from Earth. It appears quite thin and has a dark dust lane.

Quasars

Quasar PG1247+26° is the brightest quasar visible in Coma Berenices. As well, W Com was originally identified as a variable star and so given a variable star designation, but later discovered to be a BL Lacertae object. It is normally around magnitude 16.5 m, but has been known to reach 12th magnitude.

Globular clusters

M53 (NGC 5024) is a globular cluster that was discovered by Bode in 1775 and independently by Charles Messier in February 1777. Its brightness is 7.7^m, making it visible in binoculars. It is around 65,000 light years away and its total luminosity is around 200,000 times that of the Sun. Only 1° away is NGC 5053, a globular cluster that is sparser and has a less dense nucleus of stars. Its total luminosity is around 16,000 suns, which is one of the lowest luminosities of any globular cluster. It was discovered by Sir William Herschel in 1784. It is around magnitude 9.9 m. NGC 4147 is a somewhat dimmer (magnitude 10.2m) globular cluster with a much smaller apparent size.

History and mythology

Coma Berenices has been known as a distinct asterism since the Hellenistic period. Eratosthenes referred to it as both "Ariadne's Hair" and "Berenice's Hair". Ptolemy referred to it as "the lock" (of hair); however, he did not list it as one of his 48 constellations, considering it as part of Leo. For many years, Coma Berenices was considered usually as the tuft in Leo's tail, or sometimes as part of Virgo.

During the 16th century, a few maps that were made of the sky pictured two new constellations, including Coma Berenices. Tycho Brahe, who is usually given credit for the creation of the constellation, listed it as a distinct constellation in his star catalogue of 1602, and it appeared in Johann Bayer's Uranometria of 1603.

Even though this constellation is a modern constellation, it is associated with a charming legend. It is one of the few constellations (with Scutum) to owe its name to a historical figure, in this case Queen Berenice II of Egypt, wife of Ptolemy III Euergetes (fl. 246 BC–221 BC), the king under whom Alexandria became an important cultural center.

Circa 243 BC, the king undertook a dangerous expedition against the Syrians, who had murdered his sister. Berenice swore to the goddess Aphrodite to sacrifice her famous long hair, of which she was extremely proud, if her husband returned safely. He did, and she had her hair cut and placed it in the goddess' temple.

By the next morning the hair had disappeared. To appease the furious king and queen (and save the lives of the temple priests), the court astronomer, Conon, announced that the offering had so pleased the goddess, that she had placed it in the sky. He indicated a cluster of stars that at the time were identified as Leo's tail, but which have since been called Berenice's Hair. (Cf. Gaius Julius Hyginus, Astronomica 2.24)

References

• Burnham, Robert Jr. (1966, 1978). Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, v.2. General Publishing Company, Ltd., Toronto. ISBN 0-486-23567-X.
• The Deep Photographic Guide to the Constellations: Coma Berenices
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0007251209. Princeton University Press, Princeton. ISBN 978-0691135564.

External links

• Star Tales – Coma Berenices