Degree of difficulty 3 (of 5)

Minimum aperture 50mm

Designation NGC 6838

Type Globular cluster

Class XI

Distance 18,330 ly (R2005) 16,050 ly (CMD, 2004)

Size 40 ly

Constellation Sagitta

R.A. 19h 53.8min

Decl. +18° 47′

Magnitude 8.0

Surface brightness –

Apparent diameter 7,2′

Discoverer de Chéseaux, 1746

History M 71 was discovered in 1745 or 1746 by the Swiss amateur astronomer Phillipe Loys de Chéseaux. It received No. 13 in his short list of nebulous stars, which, unfortunately, was only read before the Paris Academy of Sciences and was never published in print. Hence, this and all other observations of de Chéseaux were soon forgotten.

A new discovery of this object was made by Johann Gottfried Köhler in Dresden, Germany, some time between 1772 and 1779. He described it as a “very pale nebulous patch in Sagitta.” Köhler's observations took a long time to become known in France. Even the third discovery of M 71, on the 28th of June 1780, by Pierre Méchain, must be regarded as independent. He delegated his find to Charles Messier, who remarked on the 4th of October 1780: “it is very faint and does not contain any star.”

William Herschel was able to resolve this globular cluster into individual stars, and his son John characterized it very nicely: “Irregularly round cluster of very small stars, inclining to triangular form.” In a more extended description written in 1830, he also said: “A fine object; stars of 11th to 16th magnitude; the most condensed part is 3' in diameter, of a triangular figure, the angle northward.” Webb commented that in his 3.7-inch refractor, M 71 appeared “hazy to low power, yielding to a cloud of faint stars to higher powers.”

On the first photographs of the early twentieth century, Curtis spotted only a “rather sparse globular cluster 5' in diameter.”

Astrophysics Is M 71 an old, compact open cluster, or a loose globular cluster? This question remained unsolved for many decades and is sometimes debated still today.