I'm thinking what we're seeing here is motion blur from the low light conditions. Although I would have to applaud you for not using a flash (or it doesn't appear like you did) I would like to suggest using a tripod, and a timed shutter. Even when you have a tripod, in low light an long exposure shots its very likely to get motion blur still. This is why timed shutter is very helpful , because you press the button can get clear of the camera so it can settle and then the shutter snaps.