William Herschel discovered NGC 6158 = H II-647 on 17 Mar 1787 (sweep 715) and recorded "F, S, iF. Discovered with 300, but I could see very well with the sweeping power. The time inaccurate." His rough position is ~1 min of RA east of CGCG 224-031 = PGC 58198. Herman Schultz measured an accurate position (used in the NGC) at the Uppsala Observatory.

300/350mm - 13.1" (5/26/84): faint, very small, round. Located 2.1' NW of a mag 10 star and 5.3' N of a second mag 10 star. Brighter than the faint companions of NGC 6166. Located 14' SW of NGC 6166 in AGC 2199.

400/500mm - 18" (8/12/10): fairly faint, small, slightly elongated E-W, 25"x20", sharply concentrated with a very small bright core. PGC 58195, an extremely faint companion, is just 28" SE.

Notes by Steve Gottlieb