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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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