John Herschel discovered NGC 3909 = h3364 on 1 Mar 1835 and logged "a fine, large, but coarse cl class VII; stars 9, 10, 11m; two double stars are in it." On a later sweep he recorded "Place of a double star in a vL, no v comp cl, class VII, well defined and insulated, has about 50 or 60 st 9...12 m". His position corresponds with a pair of mag 10-11 stars at 18" separation in a scattered group. RNGC classifies this number as nonexistent (Type 7).

300/350mm - 14" (4/5/16 - Coonabarabran, 73x and 145x): at 73x, this very large, scattered cluster contained ~75 stars mag 10-14 in a 20'x14' field, elongated E-W. Many of the stars are arranged in a roughly circular (somewhat boxy) annulus, with relatively few stars in the interior. Stands out reasonable well at low power, but unimpressive at 145x. On the west side is HJ 4476, a 10.1/11.0 pair at 20". A couple of doubles are on the east side, including a 13th mag pair at 14", and near the center is a mag 10.2/11.8 pair at 25".

Notes by Steve Gottlieb