William Denning discovered IC 166 around 1890 with his 10-inch With-Browning reflector. The discovery was communicated directly to Dreyer. The IC position corresponds with the faint open cluster Tombaugh 3 = OCL-334 = Lund 60.

Clyde Tombaugh independently found IC 166 in Jan/Feb of 1941 while surveying the circumpolar region from Lowell Observatory with the 13-inch Lowell telescope. He tentatively identified "Tombaugh 3" as an open cluster, though thought is might be a loose globular or "even a midget galaxy just beyond the border of our Milky Way System".

400/500mm - 17.5" (8/5/97): position identified at 100x using a GSC chart, although only a couple of stars are plotted. Appears as a very faint circular glow with a couple of faint stars superimposed. Located 7' E of a wide pair of mag 9/11 stars [at 38" separation]. Does not resemble a cluster in appearance and would have otherwise thought this was a Milky Way patch. At 220x, the glow is ~4' in diameter and there are a sprinkling of ~10 very faint stars, mostly mag 14.5-15.5 with one mag 13 star. The glow has an irregular surface brightness with a mottled appearance and the periphery is not well defined.

Notes by Steve Gottlieb