Motion and the Sun · Beginner
Mercury retrograde
Mercury's apparent backward motion, about three times a year for roughly three weeks.
It happens because Mercury, on its inside track, catches up with and passes Earth, so its direction against the stars seems to reverse. In popular astrology it is blamed for miscommunication and travel delays; that is a folk belief with no physical mechanism behind it.
Sources
Written for Cool Moon Facts in its own words. An astrology source documents what astrologers believe or practise; it does not establish that astrology works.