The Coma Berenices is an ancient asterism in the northern sky which has been defined as one of the 88 modern constellations. It is located in the fourth galactic quadrant, bordered by Bootes to the east, Canes Venatici to the north, Leo to the west and Virgo to the south. Covering 386.5 square degrees and 0.937% of the night sky, it ranks 42nd of the 88 constellations in size. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 12 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 11h 58m 25.09s and 13h 36m 06.94s, and the declination coordinates are between +13.30° and +33.31°. Coma Berenices is wholly visible to observers north of latitude 56°S. And the constellation’s midnight culmination occurs on 2 April and is visible in both hemispheres. Its name means “Berenice’s Hair” in Latin and refers to Queen Berenice II of Egypt, who sacrificed her long hair as a votive offering. It was introduced to Western astronomy during the third century BC by Conon of Samos and was further corroborated as a constellation by Gerardus Mercator and Tycho Brahe. Coma Berenices is the only modern constellation named for a historic figure.
Coma Berenices is not particularly bright, as none of its stars is brighter than the fourth magnitude, although there are 66 stars brighter than or equal to apparent magnitude 6.5. The constellation’s brightest star is Beta Comae Berenices (43 Comae Berenices in Flamsteed designation, occasionally known as Al-Dafira), at magnitude 4.2 and with high proper motion. In Coma Berenices’ northeastern region, it is 29.78 ± 0.05 light-years from Earth. A solar analogue, it is a yellow-hued F-type main-sequence star with a spectral class of F9.5V B. Beta Comae Berenices is around 36% brighter, 15% more massive than the Sun, and with a radius 10% larger. The second-brightest star in Coma Berenices is the 4.3-magnitude, bluish Alpha Comae Berenices (42 Comae Berenices), with the proper name Diadem, in the southeastern part of the constellation. Despite its Alpha Bayer designation, the star is dimmer than Beta Comae Berenices. It is a double star, with the spectral classes of F5V and F6V. The star system is 58.1 ± 0.9 light-years from Earth. Gamma Comae Berenices (15 Comae Berenices) is an orange-hued giant star with a magnitude of 4.4 and a spectral class of K1III C. In the southwestern part of the constellation, it is 170 ± 7 light-years from Earth. Estimated to be around 1.79 times as massive as the Sun, it has expanded to around 10 times its radius. It is the brightest star in the Coma Star Cluster. With Alpha Comae Berenices and Beta Comae Berenices, Gamma Comae Berenices forms a 45-degree isosceles triangle from which Berenice’s imaginary tresses hang.
The star systems of Coma Berenices include binary, double and triple stars. 21 Comae Berenices (proper name Kissin) is a close binary with nearly-equal components and an orbital period of 26 years. The Coma Cluster contains at least eight spectroscopic binaries, and the constellation has seven eclipsing binaries. There are over thirty double stars in Coma Berenices, including 24 Comae Berenices with contrasting colours. Its primary is an orange-hued giant star with a magnitude of 5.0, 610 light-years from Earth, and its secondary is a blue-white-hued star with a magnitude of 6.6. Triple stars include 12 Comae Berenices, 17 Comae Berenices, KR Comae Berenices and Struve 1639. Over 200 variable stars are known in Coma Berenices, although many are obscure.
Some supernovae have been discovered in Coma Berenices. Four (SN 1940B, SN 1969H, SN 1987E and SN 1999gs) were in the NGC 4725 galaxy, and another four were discovered in the M99 galaxy (NGC 4254): SN 1967H, SN 1972Q, SN 1986I and SN 2014L. Five were discovered in the M100 galaxy (NGC 4321): SN 1901B, SN 1914A, SN 1959E, SN 1979C and SN 2006X.
Coma Berenices has seven known exoplanets. One, HD 108874 b, has Earth-like insolation.
The Coma Star Cluster doesn’t have a Messier or NGC designation, but is in the Melotte catalogue of open clusters (designated Melotte 111). Catalogued as Collinder 256, it is a large, diffuse open cluster of about 50 stars ranging between magnitudes five and ten, spread over a huge region (more than five degrees across) near Gamma Comae Berenices. It has such a large apparent size because it is relatively close, only 288 light-years away. There are several globular clusters, including M53 (NGC 5024) which was discovered by Johann Elert Bode in 1775 and Charles Messier in February 1777; William Herschel was the first to resolve it into stars. The magnitude-7.7 cluster is 56,000 light-years from Earth. Only 1° away is NGC 5053, a globular cluster with a sparser nucleus of stars. Its total luminosity is the equivalent of about 16,000 suns, one of the lowest luminosities of any globular cluster. It was discovered by William Herschel in 1784. NGC 4147 is a somewhat dimmer globular cluster, with a much-smaller apparent size.
The Coma Supercluster, itself part of the Coma Filament, contains the Coma and Leo Cluster of galaxies. The Coma Cluster (Abell 1656) is 230 to 300 million light-years away. It is one of the largest known clusters, with at least 10,000 galaxies (mainly elliptical, with a few spiral galaxies). Its brightest members are NGC 4874 and NGC 4889, both with a magnitude of 13; most others are magnitude 15 or dimmer. NGC 4889 is a giant elliptical galaxy with one of the largest known black holes (21 billion solar masses), and NGC 4921 is the cluster’s brightest spiral galaxy. After observing the Coma Cluster, astronomer Fritz Zwicky first postulated the existence of dark matter during the 1930s. The massive galaxy Dragonfly 44 discovered in 2015 was found to consist almost entirely of dark matter.
Coma Berenices contains the northern portion of the Virgo Cluster (also known as the Coma–Virgo Cluster), about 60 million light-years away. The portion includes six Messier galaxies. M85 (NGC 4382), considered elliptical or lenticular, is one of the cluster’s brighter members at magnitude nine. M85 is interacting with the spiral galaxy NGC 4394 and the elliptical galaxy MCG-3-32-38. M88 (NGC 4501) is a multi-arm spiral galaxy seen at about 30° from edge-on. It has a highly-regular shape with well-developed, symmetrical arms. Among the first galaxies recognized as spiral, it has a supermassive black hole in its centre. M91 (NGC 4548), a barred spiral galaxy with a bright, diffuse nucleus, is the faintest object in Messier’s catalogue at magnitude 10.2. M98 (NGC 4192), a bright, elongated spiral galaxy seen nearly edge-on, appears elliptical because of its unusual angle. The magnitude-10 galaxy has no redshift. M99 (NGC 4254) is a spiral galaxy seen face-on. Like M98 it is of magnitude-10 and has an unusually long arm on its west side. M100 (NGC 4321), a magnitude-nine spiral galaxy seen face-on, is one of the cluster’s brightest.
M64 (NGC 4826) is known as the Black Eye Galaxy because of the prominent dark dust lane in front of the galaxy’s bright nucleus. Also known as the Sleeping Beauty and Evil Eye galaxy, it is about 24 million light-years away. Recent studies indicate that the interstellar gas in the galaxy’s outer regions rotates in the opposite direction from that in the inner regions, leading astronomers to believe that at least one satellite galaxy collided with it less than a billion years ago. All other evidence of the smaller galaxy has been assimilated. At the interface between the clockwise- and counterclockwise-rotating regions are many new nebulae and young stars.
NGC 4314 is a face-on barred spiral galaxy at a distance of 40 million light-years. It is unique for its region of intense star formation, creating a ring around its nucleus which was discovered by the Hubble Space Telescope. The galaxy’s prodigious star formation began five million years ago, in a region with a diameter of 1,000 light-years. The core’s structure is also unique because the galaxy has spiral arms which feed gas into the bar.
NGC 4414 is an unbarred spiral flocculent galaxy about 62 million light-years away. It is one of the closest flocculent spiral galaxies.
NGC 4565 is an edge-on spiral galaxy which appears superimposed on the Virgo Cluster. NGC 4565 has been nicknamed the Needle Galaxy because when seen in full, it appears as a narrow streak of light. Like many edge-on spiral galaxies, it has a prominent dust lane and a central bulge.
NGC 4651, about the size of the Milky Way, has tidal stellar streams gravitationally stripped from a smaller, satellite galaxy. It is about 62 million light-years away.
NGC 4676, sometimes called the Mice Galaxies, is a pair of interacting galaxies 300 million light-years from Earth. Its progenitor galaxies were spiral, and astronomers estimate that they had their closest approach about 160 million years ago. That approach triggered large regions of star formation in both galaxies, with long “tails” of dust, stars and gas. The two progenitor galaxies are predicted to interact significantly at least one more time before they merge into a larger, probably-elliptical galaxy.
The Coma Berenicids meteor shower peaks around 18 January. Despite the shower’s low intensity (averaging one or two meteors per hour), its meteors are some of the fastest, with speeds up to 65 km/s (40 mps). Credit: Wikipedia.