William Herschel possibly discovered IC 3668 = Wolf V-2 on 9 Apr 1787 in his observation of NGC 4618. He recorded "Two. The most north considerably or vB. The most south pB. Their nebulosities run into each other; the most north vmbM." The southern object may be IC 3668, the HII complex on the south end of the galaxy . John Herschel also called this galaxy double. On 12 Apr 1830 he logged, "Double; a B, L nebula, gbM, with a F one attached, 70° sf, so as to run together into one; moonlight." JH included two GC designations, but Dreyer combined them in the NGC. NGC 4618 was observed several times at Birr Castle and two knots were clearly noted on the south side, probably IC 3668 and 3669. On 10 Apr 1855, R.J. Mitchell wrote, "The s branch is patchy, having 2 B spots near p end." Three nights later he added "Seen as before, I susp a * in the f of the 2 knots in s branch." On 27 Mar 1868, C.E. Burton remarked, "The s end of annulus suspected to have two B patches in it." Max Wolf independently discovered IC 3668 on a Heidelberg plate taken 21 Mar 1903 and is credited in the IC. He noted "pF, pS, iF, N."

400/500mm - 18" (5/15/10): extending mostly to the south side of the central bar of NGC 4618 is a faint, beefy arm that often appears detached and barely connected on the east end of the central region. This broad arm winds counterclockwise from east to south roughly 100° with IC 3668, the brightest region or knot, near the south end of the arm, ~1.8' from the center of the bar.

900/1200mm - 48" (4/7/13): IC 3668 is a bright, elongated HII region(s) at the south end of the singe prominent arm of NGC 4618 = Arp 23, ~20"x10". Situated 1.7' S of center.

Notes by Steve Gottlieb