William Herschel discovered NGC 5905 = H II-758 on 5 May 1788 (sweep 842) and logged " pF, pS, iR." His position (offset from another galaxy) is 42 sec of RA too far west. NGC 5905 and 5908 were observed at Birr Castle on 13 Apr 1850 and assumed to be novae, so John Herschel assigned a separate General Catalog designation (4084). Dreyer combined the two GC designations in the NGC and reported an accurate position measured by d'Arrest.

300/350mm - 13" (6/4/83): fairly faint, moderately large, slightly elongated ~N-S, diffuse halo increases to brighter core.

400/500mm - 17.5" (5/23/87): moderately bright, moderately large, bright core, elongated 3:2 NW-SE. A mag 14 star lies 1.6' E of center. NGC 5908 lies 12' SE.

600/800mm - 24" (7/28/19): at 322x; fairly bright, moderately large, 1.5' diameter, slightly elongated, sharply concentrated with a very small bright nucleus. A slightly brighter "bar" runs SW-NE through the nucleus, but the contrast is low. The halo has a fairly low surface brightness and there was only a subtle hint of spiral arms. A mag 15 star is 0.7' SW of center (in halo), a mag 15.3 star is 0.8' S of center (in halo) and a mag 14.4 star is 1.6' E of center (outside halo). A mag 11/11.5 double star (WZ 13) at 9" separation, lies 4' SSE. Member of the NGC 5908 group (LGG 395).

MCG +09-25-037, located 12' WNW, appeared very faint, fairly small,roundish, ~25" diameter, very low surface brightness, requires averted vision.

Notes by Steve Gottlieb