Mercury stations retrograde on December 3, 2017 at 29° Sagittarius, and direct on December 23 at 13° Sagittarius — 20 days. From the Earth, Mercury seems to back up against the stars as we overtake it, as a car passed on the highway seems to slide backward. Astrology holds it a time for crossed wires and delays. Computed from JPL's approximate orbits; the stations agree with an almanac's to within minutes.