Object of the Week April 30, 2017 - The Coma Star Cluster
Coma Star Cluster, Mel 111, Collinder 256
Type: Open Star Cluster
Constellation: Coma Berenices
RA: 12h 25m 57s
Dec: +26° 00’ 19.4”
Magnitude: 1.79
An all too short trip this week afforded me a brief opportunity to do some rich-field observing from the South rim of Canyon de Chelly (Chinle, Arizona) altitude 5,500’ and from Hannigan’s Meadow, Arizona (AZ) altitude of 9,100’. Hannigan’s Meadow is 70 miles and several mountain ranges from any measurable population center (Clifton, AZ) making it a very dark site. Regretfully my exhaustive itinerary and the First Quarter Moon conspired to keep me from experiencing these truly dark sites without moonlight. Nonetheless it was a truly an amazing experience scanning these skies with binoculars and a small refractor. Next time I travel to Hannigan’s Meadow I’ll be sure to bring my 15” Obsession Classic and will stay for several nights around the New Moon.
Despite the moonlight this week’s Object of the Week, the Coma Star Cluster in the constellation Coma Berenices, was readily visible to the naked eye. This large and conspicuous cluster was first described by Ptolemy around 135 AD. The cluster had always been associated with Leo’s tail, but Ptolemy renamed it for the Egyptian queen Berenice’s legendary sacrifice of her hair.
Yet as conspicuous as this cluster is in the night sky, it never was given a Messier or NGC number. The 19th century astronomy popularizer, Garrett P. Serviss, described it as “gossamers spangled with dewdrops.” British astronomer P.J. Melotte cataloged it in 1915 as #111 in his catalog of star clusters. It was not until 1937 that the Swiss-American astronomer R.J. Trumpler demonstrated that this was a true physical cluster.
At a distance of 288 light years, the Coma Star Cluster is one of the third closest star cluster to us. This explains why its stars are appear widely separated over a nearly 5° field. The cluster is known to contain about 80 stars between the magnitudes of 4.5 to 10.5.
A rich field instrument with a 3° to 6° field of view is the best way to observe this cluster. In binoculars more than a dozen of the brightest members of the cluster are easily seen appearing to float in the foreground while many more of the dimmer stars appear to fill out the background.
For those observing with large aperture instruments you’ll find several bright galaxies within the vicinity of the Coma Star Cluster. These include the magnitude 9.2 spiral galaxy, NGC 4565 that is also known as the Needle Galaxy and the magnitude 9.8 elliptical galaxy, NGC 4494. Close to the 4.96 magnitude star, 16 Coma Berenices or SAO 82314, you’ll find the galaxy PGC 4547332 listed, perhaps erroneously, as a relatively bright 10.8 magnitude galaxy.
Give it a go and let us know!
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