My best understanding has been that it is comparable to those who swear by the zodiac to understand personality, medical cures, and whatever other superstitions are attached. [His interest has been minimal, and those opportunities to be out of the cells and in the library have seen Alucard focus on maps and history more than what he's dismissed as a pointless system.

Maybe he should re-evaluate that determination. And maybe make it less clear how old he is, given medical astrology is well out of date.]

This is all also presuming you were given the same nonsense explanation as we were, of course.