Apparent retrograde motion: why planets seem to move backwards

An overtaking illusion

Planets move eastward against the stars most of the time. But Earth is moving too. When Earth overtakes an outer planet such as Mars, Jupiter or Saturn — around the time the planet is opposite the Sun in our sky — that planet appears to slow, stop (a station), drift westward and then resume. Mercury and Venus show the same effect when they overtake Earth on the inside, around the time they pass between Earth and the Sun.

The Sun and the Moon never appear retrograde. The mean lunar nodes, Rahu and Ketu, always move westward.

Retrograde windows in the coming year

The pattern repeats on regular timescales: Mercury about three times a year for around three weeks, Venus every nineteen months or so for about six weeks, Mars every two years or so for two to three months, Jupiter and Saturn once a year for four to five months.

Vakri grahas in Jyotish

Jyotish calls a retrograde graha vakri and gives it particular weight; classical strength calculations include its motion. Interpretations differ between schools, and they are tradition, not astronomy. In the 3D Kundli table, the Motion column marks each graha as direct or retrograde from its calculated daily motion.

Watch it happen in the Observatory: its retrograde lesson shows Earth overtaking Mars from above and from the ground.