M71
NGC 6838
Properties
Position & Identifiers
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M71 · 6.9′ diameter · N up, E left
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About M71
Description
M71 is an unusual cluster in Sagitta, about 12,000 light-years from Earth. Long debated as either a dense open cluster or a loose globular cluster, it is now classified as a globular — one of the loosest and most metal-rich known. It spans about 27 light-years and contains several thousand stars, far fewer than typical globulars.
Observing Tips
Located in the middle of the small constellation Sagitta (the Arrow), roughly midway between Gamma and Delta Sagittae. In binoculars it appears as a faint, irregular hazy patch. A 4-inch telescope at 60-80x shows a loose, mottled glow that looks more like a dense open cluster than a globular. Individual stars are resolved even in small telescopes due to its loose structure. Best observed from July through October.
History
Discovered by Philippe Loys de Cheseaux in 1745-46 and independently found by Johann Gottfried Koehler around 1775. Charles Messier cataloged it on October 4, 1780. Its classification was debated for over two centuries before modern studies confirmed it as a globular cluster.
Fun Facts
M71 blurs the line between globular and open clusters. At about 9 billion years old, it is much younger than typical globulars (which are usually 12-13 billion years). Its high metallicity and loose structure once led many astronomers to classify it as an open cluster, making it a fascinating case study in stellar classification.