William Herschel discovered NGC 6520 = H VII-7 = h3721 on 24 May 1784 (sweep 224) and recorded "a cluster of stars, chiefly large ones; considerably rich, but rather coarsely scattered; a little more compressed towards the middle. It is visible in the finder." Nearly 5 minutes earlier, he noted "Daylight very strong", though observed a couple more objects.

400/500mm - 17.5" (7/8/94): striking cluster following the remarkable dark nebula B86. Roughly 75 stars are visible in a 6' diameter. The "Inky" black dark nebula B86 to the east wraps around the cluster like a tentacle along the south side and also appears to wind through a large portion of the cluster. In the cluster's core is a very dense perfectly circular group of about two dozen stars in a 1.5' diameter punctuated with the brightest star at the exact center! Enveloping this core is a dark void except for a few stars that break through to the north. Surrounding this irregular dark annulus is a 6' incomplete oval ring formed by six brighter and several fainter stars. Located in a rich star field. Globular clusters Djorgovski 2 lies 21' WNW and NGC 6540 is 37' ENE!

Notes by Steve Gottlieb