Degree of difficulty 4 (of 5)

Minimum aperture 50mm

Designation NGC 6981

Type Globular cluster

Class IX

Distance 58,510 ly (R2005) 62,750 ly (RR Lyr, 2001)

Size 100 ly

Constellation Aquarius

R.A. 20h 53.5min

Decl. –12° 32′

Magnitude 9.2

Surface brightness –

Apparent diameter 6′

Discoverer Méchain, 1780

History It was Pierre Méchain who discovered M 72 on the night of the 29th to the 30th of August 1780. He reported his find to Messier who observed it on the 4th /5th of October the same year and described it as a “nebula, its light faint as the previous [M 71], near it is a telescopic star.”

Three years later, William Herschel recognized the true nature of this globular cluster. In 1810, the great observer described at length how M 72 looked to him at 280× magnification: “It is a cluster of stars of a round figure, but the very faint stars on the outside of globular clusters are generally a little dispersed so as to deviate from a perfectly circular form. It is very gradually extremely condensed in the center, but, with much attention, even there, the stars may be distinguished. It is not possible to form an idea of the number of stars that may be in such a cluster; but I think we cannot estimate them by hundreds.”

His son John agreed with that in his first note on this cluster: “Pretty bright; very compressed cluster; irregularly round; barely resolved; very gradually brighter toward the middle; resolved into very small stars; many straggling stars near, but none so small as those of the cluster.” But after a later observation of M 72, he had a somewhat different impression: “Faint; round; 2' diameter; resolvable, but I do not see the stars separated enough to count them. Is rather an insignificant object.”

Admiral Smyth, who was in close contact with John Herschel, saw M 72 resolved in his 5.9-inch refractor as a “globular cluster of minute stars.”