Sorry, astrologers -- this is what it really means when a planet is in…

You usually hear about a planet being "in retrograde" from astrologers, which might give you the impression that the term is mystical jargon. In fact, it does have an astronomical meaning. That meaning just happens to come from a rather outdated concept, when the Earth was still the center of the solar system. Today,… » 3/11/13 10:00am 3/11/13 10:00am