The cluster was discovered by wealthy Swiss landowner Philippe Loys de Cheseaux in 1746 and subsequently re-discovered by Johann Koehler in 1775 and Pierre Méchain in June 1780. Méchain informed his friend Messier who searched for the cluster, found it and catalogued it on October 4, 1780. He described it as "very faint…containing no stars…the least light extinguishes it". The view through today's high quality backyard telescopes is much better than what Messier could achieve.
M71 is very easy to locate as it lies midway between gamma Sagittae (γ Sge - mag. +3.5) and delta Sagittae (δ Sge - mag. +3.7). These stars form part of the distinctive, although not particularly bright, arrow asterism. Two degrees southwest of γ Sge is M71.
The cluster is best placed in the sky during the months of June, July and August.
Through binoculars, M71 appears as a dim but reasonably large fuzzy patch of light. It's a faint object for small telescopes that's best seen with averted vision. Through 80mm (3.1-inch) scopes very little detail is discernible, but increasing the aperture by just a small amount does make a marked improvement. With 150mm (6-inch) or 200mm (8-inch) reflectors, this globular appears large and loose with many 11th and 12th magnitude stars resolvable across the complete face. Comparisons are often made with M11, the larger and brighter Wild Duck open cluster. It's easy to see why, and M71 was earlier thought to be a very rich open cluster and not a globular cluster.
Through larger instruments many more stars are revealed. A 300mm (12-inch) reflector resolves over 100 stars across a seven arc minute diameter disk. It's also apparent that M71 lacks the typically strong central condensation of most globulars.
M71 is one of the smallest and youngest globulars known and also one of the nearest at 13,000 light-years distant. It has a spatial diameter of only 27 light-years and is estimated to be 9.5 billion years old. In total, it contains at least 20,000 stars.
M71 Data Table
|Object Type||Globular Cluster|
|RA (J2000)||19h 53m 46s|
|DEC (J2000)||18d 46m 42s|
|Apparent Size (arc mins)||7.2 x 7.2|
|Age (years)||9.5 Billion|
|Number of Stars||>20,000|
|Other Name||Collinder 409|
|Notable Feature||The irregular variable star Z Sge (Z Sagittae) is a member of this cluster|