Lawrence Parsons, 4th Earl of Rosse, discovered NGC 3999 on 25 Apr 1878 in one of the six Birr Castle observations of the NGC 4005 cluster. Parsons placed this nebula at 277" separation in PA 201.3° (SSW) with respect to mag 8 HD 103913 and it was labeled as Mu on the composite sketch of the cluster. At this exact offset is CGCG 127-117 = PGC 37647. The RNGC position is clearly in error and points to a blank piece of sky (closer to NGC 4011). Listed in my RNGC Corrections #3.

400/500mm - 17.5" (4/18/98): extremely faint, very small, round, 15" diameter. Requires averted vision and can only hold steadily 2/3 of the time. A mag 12 star is 1.5' preceding. Located 4.6' SSW of mag 7.4 SAO 82077 in the NGC 4005 cluster. The RNGC identification is incorrect.

600/800mm - 24" (3/22/14): very faint, very small, round, 15" diameter, even surface brightness. Situated 1.4' E of a mag 12 star and 4.5' SSW of mag 8 HD 103913. A string of gaalxies oriented NW to SE begins with NGC 4000, which lies 4.5' N.

Notes by Steve Gottlieb