William Herschel discovered NGC 5903 = H III-139 = h3598, along with NGC 5898, on 21 May 1784 (sweep 222) and recorded both as "Two, vF, R nebula, not vS, about 7' distance from each other and nearly in the same parallel." JH logged "B; R; pgbM; 20"." Vincenzo Cerulli measured an accurate micrometric position although Dreyer didn't publish his corrected position in the IC II notes.

200/250mm - 8" (7/5/83): very faint, round, nice pair with NGC 5898.

300/350mm - 13.1" (7/5/83): moderately bright, small, round. Appears similar to NGC 5898 5.5' SW but slightly larger.

400/500mm - 18" (6/22/09): moderately bright, moderately large, elongated 3:2 ~N-S, 1.1'x0.8', contains a bright core that gradually increases to the center, faint stellar nucleus. A mag 12.3 star is off the NW side, 1.5' from center. Forms a trio with NGC 5898 5.5' SW and ESO 515-003 3.1' S.

18" (6/17/04): moderately bright, moderately large, 1.2'x1.0', well-concentrated with a bright 20" core. Slightly fainter than NGC 5898 5.5' SW.

Notes by Steve Gottlieb