Is Mercury in retrograde?

Mercury retrograde is an optical illusion. Three or four times a year, as the faster-orbiting Mercury overtakes Earth on the inside track, the planet appears — from our point of view — to slow down, stop, and move backwards (westward) against the background stars for about three weeks before resuming its normal eastward motion.

Nothing actually reverses: Mercury keeps orbiting the Sun the same way. The "backward" motion is purely a line-of-sight effect, the same reason a faster car you overtake on the motorway seems to drift backwards.

The dates above are computed from Mercury’s geocentric apparent longitude (the moment its motion is stationary), corrected for light-travel time, in Universal Time (UT). Different sources may differ by a day depending on time zone.