DSO of the Month
Double Cluster (Caldwell 14; NGC 869 and NGC 884)
Due south at 20.45 (GMT) on 15 December
Position: 02 hr 20 min +57 deg 08 min
Image: William Wood (HAS)
There are not many deep sky objects which can be seen with the naked eye. This also means that there were not many deep sky objects which were discovered before the telescope came into use. But “not many” is not the same as none. To be sure in the light polluted skies of Havering we can only see a few. There are the Pleiades (M45), the Orion Nebula (M42) and I have seen the Hyades on rare occasions when the night has been particularly clear. But I have not been able to see the Andromeda Nebula for example. Another deep sky object which is perfectly clear in dark skies but not in Havering (alas!) is the Double Cluster. Yet in the dark skies of Suffolk (for example) one can look up and see the Double Cluster looking like a pair of round owl’s eyes. They are close together as we see them, unusually they are actually close together in space, both being 7,600 light years away from us and a few hundred light years apart. They are both are very young clusters, “only” 12.5 to 13 million years old. By comparison the still young Pleiades cluster is about 115 million years old. Yet visually the two clusters are very different, NGC 869 (on the right in the picture) is compact whereas NGC 884 is rather loose without a clearly defined centre. The existence of the double cluster as a fuzzy patch was known to the ancient Greeks but obviously it was only after the invention of the telescope that it became obvious that it was made up of two star clusters. Personally I would say that they are obviously two patches with the naked eye (in dark skies), but perhaps the old astronomers failed to notice this. The old name for this pair was the Sword Handle of Perseus, based on the drawings of Perseus as a constellation (also see the Star of the Month). It was only when the pictorial versions of the constellations fell out of use that the modern name became common at the end of the nineteenth century. The Double Cluster is easy to find (in light polluted skies, in dark skies it is easily seen between Perseus and Cassiopeia) by taking the line between Gamma and Delta Cassiopeiae (the downstroke of the W of Cassiopeia so to speak) down until it reaches a straight line up from the bright star Alpha Persei (Mirphak). Each cluster is about half a degree wide and about a degree apart, they are best seen in binoculars rather than a telescope.
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