DSO of the Month
Coma Berenices Cluster
AKA: Melotte 111 and Collinder 256
Due south at 23.50 (BST) on 15 April
Position: 12 hr 25 min +26 deg 06 min
Image: Simbad (http://simbad.u-strasbg.fr/simbad/)
Most star clusters such as the Pleiades or the Beehive Cluster, have a Messier or NGC designation, a clear shape and while large compared with other deep sky objects, they are relatively small compared with the size of the constellations. There is one cluster which breaks all these rules, namely the hair of Queen Berenice or to give the Latin name, the Coma Berenices Cluster. It is called Melotte 111 or if you prefer Collinder 256. It is hard to give a definite size as it is a loose scattering of stars, but Wikipedia gives a size of 7.5 degrees. It is 280 light years away which means it is closer than either the Pleiades (450 ly) or the Beehive Cluster (607 ly) and with an age of 450 million years it is middle aged, lying between the young Pleiades (115 million years) and the old Beehive (600 million years). The ancient astronomer Ptolemy identified Gamma (mag. 4.4), 7 (4.9) and 23 (4.8) Comae Berenices as the core of the cluster (although obviously not under these designations) and he described as being ivy-shaped. It does indeed form a vaguely V or W shape outlined by its stars. To find the cluster, look for a right-angle triangle of stars made up of Alpha, Beta and Gamma Comae Berenices between Leo and Boötes (or between Denebola and Arcturus). It will not be easy to make out this grouping in Havering as they are all roughly magnitude 4.3. Gamma is the western-most or rightmost star (i.e. the one nearest Leo) and the cluster lies directly underneath it. Given its size, it is best viewed in 10x50 binoculars or the finderscope of a telescope rather than a telescope.
Berenice was the wife of the Hellenistic Egyptian pharaoh Ptolemy III Euergetes (c.280-222 BC) in the middle of the third century BC. Ptolemy III invaded the neighbouring Seleucid Empire in 246 BC and Berenice promised to cut off her hair and place it in a temple near modern-day Aswan if he was in successful in the war. Her husband captured Babylon and regarded himself as the victor. Berenice duly placed her locks in the temple, but they disappeared. To console the queen, the astronomer Conon of Samos (c.280–c.220 BC) said that the tresses had been placed in the sky by the gods. The cluster he identified as being Berenice’s hair had hitherto been regarded with some logic as being the bushy tail of the Lion. The famous Hellenistic poet Callimachus (c. 310/305-240 BC) commemorated the story in a collection of poems called Aetia (Causes). However Coma Berenices only became a recognised constellation in the 16th century.
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