Thats funny.... last weekend I too had a peek at Joops through my 12"LB and I SAW THE SAME THING I counted the moons and I could see 4 - all away from Joops. I even shone my torch down the tube to see if there was muck on mirror, then I put in a different eyepiece, and it was still there a distinct round completely black shadow - towards the edge. I thought arent I clever - I have seen a transit but there are only 4 big moons arent there??? and this was the fifth
what was it??