William Herschel discovered NGC 6555 = H II-902 on 29 Jun 1799 (sweep 1090) and recorded "F, pL, R, vgbM, about 3 1/2' dia." A few minutes earlier he noted that twilight was very strong. His time is 20 seconds too small and declination 1' too far south. Herman Schultz measured a micrometric position at Uppsala (used in the NGC), but it was 40 seconds of time too small, so he probably either made a copying error or misidentified the comparison star. Bigourdan measured an accurate position on 16 Jun 1884 (repeated in the IC 2 Notes).

400/500mm - 17.5" (7/1/89): moderately bright, moderately large, almost round, mild concentration but no sharp core.

Notes by Steve Gottlieb