ABSTRACT
YO U R F R I E N D I S L AT E . You are watching TV while you wait,but are listening for the sound of someone coming up the path, or the slam of a car door. Now and again you think you hear her coming, but on looking out discover you were wrong. At last you are fairly sure you really do hear her, and go out; this time you are right, and your friend is outside. It is a clear frosty night, and you both look up to admire the stars. Although there are many bright stars, there seem to be more to the edges of the sky, but as you move your eyes to look directly at them they seem to disappear. Sometimes you think you see a faint star, but sometimes you are not sure if it really there or not. ‘One of those stars is moving, it must be a satellite or a planet,’ your friend says. You ask ‘where?’, and try to detect if one of the lights in the group pointed out is moving or not. ‘Well, I can’t see anything moving!’, you say, but you friend is quite certain that she is not imagining it. Who is right, and how can we explain some of these examples?
