IC 4665 is a widely scattered open cluster covering an area of the sky comparable to that of the Moon's disc. The cluster as a whole approaches magnitude +4.2, and is visible to the naked eye under ideal conditions. Its individual stars are fainter, with none exceeding magnitude +6.8, and so optical aid is required to see details of the cluster's structure.
IC 4665 is a cluster of about thirty stars that began to
develop less than forty million years ago, lying about 1,400 light years from
Earth in the constellation of
Ophiuchus. By comparison with most star clusters,
these figures make it very young and - relatively speaking - nearby. The cluster
is just visible to the naked eye, as a faint point of light somewhat to the south of Rasalhague.
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