William Herschel discovered NGC 5403 = H III-683 = h1726 on 16 May 1787 (sweep 738) and logged "cF, pL, iF." JH simply logged "eF; pL", and measured an accurate position. He missed the nearby companion.

400/500mm - 17.5" (5/27/95): very faint, moderately large, very elongated 3:1 NW-SE, 2.5'x0.8'. Bulging central region but overall has a low even surface brightness. Forms a close pair with NGC 5403A just 1.6' NE of center. The companion appeared very faint, small, round. Appears as a low surface brightness spot with no concentration.

900/1200mm - 48" (4/7/13): at 488x appeared bright, very large, excellent edge-on 5:1 NW-SE, 3.0'x0.6', broad concentration with a brighter, bulging, elongated core, ~25" diameter. The edge-on disc tapers towards the tips. A subtle equatorial dust lane passes just east of the core region, slicing the galaxy in half, though the section east of the dust is fainter and contains much less of the core.

NGC 5403A = CGCG 191-030 lies 1.7' NE and is angled perpendicular to the major axis of NGC 5403, on line with the core. It appeared fairly bright, fairly small, elongated 2:1 SW-NE, 0.4'x0.2', brighter core.

Notes by Steve Gottlieb