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What's in the Sky?

Thursday 17th of January

Double Cluster
The Double Cluster is the common name for the naked-eye open clusters NGC 869 and NGC 884, which are close together in the constellation Perseus.

NGC 869 and NGC 884 both lie at a distance of 7500 light years. NGC 869 has a mass of 3700 solar masses and NGC 884 weighs in at 2800 solar masses; however, later research has shown both clusters are surrounded with a very extensive halo of stars, with a total mass for the complex of at least 20,000 solar masses.

The Double Cluster is circumpolar (continuously above the horizon) from most northern temperate latitudes. It is in close proximity to the constellation Cassiopeia. The Double Cluster is approximately the radiant of the Perseid meteor shower, which peaks annually around August 12 or 13.

Although easy to locate in the northern sky, observing the Double Cluster in its two parts requires optical aid. They are described as being an "awe-inspiring" and "breathtaking" sight, and are often cited as a target in astronomy observer's guides.

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