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M47

NGC 2422

Near the northern tip of Puppis, not far from the brilliant star Sirius in the sky, lies this blue cluster. Its stars are scattered over a region roughly equivalent in apparent size to the Moon, and are bright enough to be detected by the naked eye.

Messier's forty-seventh object is an open star cluster that lies directly in the plane of the Milky Way. It is about 17° east of Sirius, and is just visible to the naked eye at magnitude +4.4. Through a telescope, M47 shares a starfield with two other open clusters, M46 and NGC 2423, but it is the brightest of these three and the nearest to Earth (about 1,500 light years away).

This is a young cluster in stellar terms. Approximately 78 million years old, it came into existence near the end of Earth's age of the dinosaurs. Because its stars are young, they still burn bright and blue; their surface temperatures are close to 20,000 Kelvin. There are about thirty stars in the cluster, spread over a region some fifteen light years across.

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