M47

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 1,600 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.