William Herschel discovered NGC 6426 = H II-587 = St VII-18 on 3 Jun 1786 (sweep 572) and recorded "F, cL, iF." His position is reasonably accurate. Stephan found the cluster 90 years later on 13 Jul 1876 and included it in his 7th list. As a result, Dreyer catalogued it again as GCS 5870, but he combined both GC entries in the NGC. Wolfgang Steinicke reports that Herschel first observed the cluster on 15 Jul 1781 with his 6.2-inch before starting his sweeps.

The position given in Sky Catalogue 2000.0, Deep Sky Field Guide (first version) and NGC 2000.0 is 10' too far south!

200/250mm - 8" (6/22/81): faint, small, round, diffuse.

400/500mm - 17.5" (5/30/92): fairly faint, 3' diameter, slightly elongated, only a weak central condensation, slightly granular. Two or three faint stars are resolved at the edge of the halo. At 286x, a few additional very faint stars are resolved over the core for a total resolution of just six stars. A striking double ∑2202 = 6.2/6.6 at 21" lies 36' S.

600/800mm - 24" (7/30/16): at 260x and 432x; fairly faint, round, moderately large, 2.5' diameter. Contains a very small, slightly brighter core that is elongated N-S and lively. A few faint stars are resolved around at the edges of the halo and several additional stars occasionally sparkle within the halo. A 15-15.5 magnitude star is at the north edge of core. In addition, five slightly brighter stars are arranged N-S along the west side of the halo; a single mag 14 star is near the NW side, two mag 14.5-15 stars on the west side, and two mag 15/15.5 stars on the SW side.

Notes by Steve Gottlieb