About 3 years ago we were cruising at 36,000 mid way on an oceanic track on HF, it was the middle of the night and I spotted a bright white light (similar to a motorcycle headlight) in the upper right had portion of the FO’s windscreen. I checked TCAS as we sometimes cross paths with other traffic but not regularly. Anyway there was nothing on TCAS and the light started getting bigger and bigger like it was coming towards us, I pointed it out to the FO and he and I watched it for the next 30 seconds or so dancing around, getting bigger then smaller etc. suddenly it seemed to come straight towards us and went straight over the top apparently so close that we both ducked :-). Didn’t see it again and at the next HF report I asked if any other traffic had been near us in the last 60 minutes, ATC said nothing else was out there that night. We agreed just to file it away under the ‘f@#k knows’ file.