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The Double Cluster in the constellation Perseus, normally known by its Greek designation transliterated. chi Persei (NGC 884, on the left) and h Persei (NGC 869) are about 7000 light-years away and less than 100 light-years apart. The Double Cluster is approaching earth at the speed of 21 km/s.

The Double Cluster is surrounded by one of the largest concentrations of red supergiants in the sky, and therefore was a fertile site of early red giant research. There are, however, an almost equal number of blue and red supergiants in the clusters.

September 13, 2010