Herschel 400 Objects

NGC 6522 & NGC 6528: Globular Clusters (Sagittarius) RA: 18h 04.2m / DEC: -30° 01'.5
Instrument: 10-inch Starfinder

Galaxy clusters are among my favorite deep-sky sights. However, a less common sight is two or more globular star clusters in the same field of view. NGC 6522 and NGC 6528 make a fine pair at 129X in my 10-inch. Their appearance is recorded in the sketch at left. The larger and brighter of the two is NGC 6522. This globular has a visual magnitude of 9.9 and features a stellar core embedded within a 5' diffuse glow. Across the field toward the northeast boundary, NGC 6528 appears as a 90" diameter patch of dull light. Surprisingly, NGC 6528 is slightly brighter at magnitude 9.6. I wonder if the outer shell is substantially fainter than the core region? This fine pair is squeezed between 3.0 magnitude Gamma Sagittarii and 4.7 magnitude HD 164975.

NGC 6520 NGC 6540


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