Coma Berenices (Latin for Berenice's Hair) is a traditional asterism that has since become a constellation. It is located near Leo, and was originally considered Leo's tail.

Notable features

Coma Berenices contains the North Galactic Pole, at right ascension 12h 51.42m and declination 27° 07.8′ (epoch J2000).

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 4.26m. It is intrinsically only a little brighter than our Sun, which gives us an idea of how faint the Sun would appear seen from only 27 light years away.

The second brightest star in Coma Berenices is named Diadem (α Comae Berenices), at magnitude 4.32m. It represents the gem in Berenice's crown. It is a double star, with two components of almost equal magnitude. It is suspected of being an eclipsing binary.

The only other fourth magnitude star in Coma Berenices is γ, at magnitude 4.36m.

Notable deep sky objects

Although Coma Berenices is not a large constellation, it contains eight Messier objects. The constellation is quite 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 (Mel 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 Comae Berenices. The cluster has such a large apparent size because it is relatively nearby, only around 270 light years away.

History and mythology

Coma Berenices has been known as an distinct asterism since ancient Greek times. Eratosthenes referred to the it as both "Ariadne's Hair" and "Berenices' 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.

Queen Berenice II of Egypt

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 Assyrians, 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.

Table of leading stars

The following table lists all stars in Coma Berenices with a Bayer designation or Flamsteed designation.

Galaxies in Coma Berenices

• Black Eye Galaxy