The problem is that if it ahppened at all, the NT makes it plain that it was a temporary event. The chief suspects for a long time were novae and supernovae, which would create a noticeable "new" star lasting a short time. Various conjunctions have been put forward (see the answerbank article) as have UFO's, the angel gabriel, in fact you name it. The point is that it may have occurred, but it stopped occuring in about 6 bc and the only people who know what the wise men from the east were following are a bunch of long dead eastern stargazers.