William Herschel discovered NGC 4458 = H II-121 = h1287 on 8 Apr 1784 and recorded (sweep 187) "Two resolvable nebula at 4 or 5' dist." He assumed one of these was M86, so only added one new discovery number. His position was ~5' west of NGC 4458 and 4461, the most likely pair. On 12 Apr 1784 he swept the field again (sweep 189) and recorded "Two [NGC 4461 and 4458]. Both pF, S, bM." His single position on this sweep was 22 sec of RA following NGC 4458 and the identification is unambiguous. JH logged "pB; R; psbM; the p of 2 [with[NGC 4461] and measured an accurate position.

On 17 Apr 1784 (sweep 199), WH recorded "two B, cL nebula" and assumed they were pair from sweep 187 (one being M86), but his position matches NGC 4435 and NGC 4438!

300/350mm - 13.1" (5/14/83): faint, small, almost round, small faint nucleus. A mag 11 star is close east.

400/500mm - 17.5" (4/25/87): moderately bright, fairly small, round, 1.0' diameter, small bright core, faint stellar nucleus. A mag 11.5 star lies 2.1' E. Forms a pair with NGC 4461 3.7' SSE. Located in the core of the Virgo cluster.

600/800mm - 24" (4/28/14): fairly bright, moderately large, round, 1.0' diameter, well concentrated with a bright core that increases to a stellar nucleus. A mag 11 star is 2' ENE. Fainter of a pair with NGC 4461 3.7' SSE.

Notes by Steve Gottlieb