I am a third year undergrad in the UK and I have been looking over my first year notes on special relativity. I found this passage talking about predictions we can derive if light is corpuscular. "If light is corpuscular (emitted like bullets) one expects the speed of light to depend on the speed of the source. Can one infer the speed of the source by measuring the speed of light? For instance the light emitted in front of a plane travelling at speed u would be travelling at speed c + u and the light emitted from the rear at speed c − u. If this was the case one could have systems of binary stars in which one star could be seen at two places at the same time." I can understand that we can take the difference between the speed of light c+u from the front of the plane and c-u from the rear and divide by two. That will give us the speed of the source, if the corpuscular nature were true. What I don't understand is how 'if this was the case one could have systems of binary stars in which one star could be seen at two places at the same time'? Any ideas?