The Double Cluster - Caldwell 14
The Double Cluster - Caldwell 14
The Double Cluster or Caldwell 14 in Perseus is a visual extravaganza and probably one of the most breath-taking sights to be seen in the night sky. On a good night the soft glow from the combined light of the two individual clusters resolve into an awe-inspiring swarm of literally dozens upon dozens of blue and white stars surrounded by just as many unrelated Milky Way stars.
The true brilliance of the Double’s stars are dimmed by swaths of heavy galactic dust clouds between ourselves and the two clusters which render their members over four times fainter than they really are. In these terms, it has been estimated that if the Double were located at a similar distance of the Pleiades (some 407 light years away), about one quarter of our northern sky would be filled by its stars and hundreds of its members would shine more brilliantly than the planet Venus.
NGC 884 and NGC 869 are located at distances of some 7,600 and 6,800 light-years from Earth respectively and thus are physically close to one another in space. Both clusters are found in the Perseus Arm of the Milky Way - we ourselves are riding the Orion Arm – and are about 5.6 million years and 3.2 million years old respectively. If we consider that an open cluster like that of Pleiades is thought of as a young cluster with about a 100 million years of age, then clearly the Double is a mere infant in cosmic terms.
The Double’s stars formed at approximately the same time and from the same primordial molecular cloud of dust and gas. Spectroscopy has revealed that many of the stars have a very high concentration of heavy elements and typically are super hot and very luminous O and B types. These massive stars are aging very quickly and few will live to a billion years; instead they will eventually self destruct into supernova, creating shock waves powerful enough to disrupt the already two loosely bound open clusters and disperse their stars. In consequence, the Double will probably be unrecognizable as a cluster within 250 million years or so.
The sketch itself was a tad complicated to complete and no doubt is not entirely accurate. These two clusters are quite complex to sketch due not only to the sheer amount of visible stars seen and the sense of differing stellar magnitude but also in the beautiful variation of colour observed at the eyepiece.
The best plan of approach was to draw up a target-clock-face with 45º angles and concentric circles and use this as a template. To achieve some sense of variation in star magnitude I used an ink-pen for the brighter stars and various grades of pencils for the dimmer stars ranging from 4B to B. Over the sketch was taped a piece of tracing paper to which I noted the more prominent star colours on the overlay. To capture the best possible field of view with the 4” f10, I used the lowest magnification I have in my collection, namely, a Celestron LX 25mm.
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