Planetary Motions

Planetary motion diagram
Planetary motion diagram
As seen from Earth, the motion of all planets is eastwards taken over the whole year. As Earth is also moving, and more quickly than the outer planets, it overtakes them around the time of opposition. At this time the outer planets appear to move backwards against the stars.
The term used to describe forward easterly direction is direct motion and backwards motion is called retrograde. The point at which the motion changes from direct to retrograde, or back again, is when a planet is said to be stationary. The position at which a planet becomes retrograde prior to opposition is the 1st stationary point and that a which it resumes direct motion following opposition is the 2nd stationary point.

In the diagram the direct motion to the east is shown at positions 1,2 and 3, backward motion to the west at 4 and 5, and direct motion to the east again at positions 6 and 7.

Oppositions (position 4) occur when an outer planet is in the opposite side of the sky from the Sun as viewed from the Earth. At opposition the planets are at their brightest. Mercury and Venus can never be at opposition since they are inside of the Earth’s orbit and, therefore, remain relatively close to the Sun. The brightest times for Mercury and Venus are close to greatest elongations.

The other side of the cycle from oppositions are conjunctions when, as viewed from Earth, a planet is in line with the Sun whose glare is too bright for the planet to be visible in the night sky.

Venus and Mercury, as inner planets, move very quickly against the constellations. They have no stationary or retrograde motion and are always seen moving easterly against the stars.

Solar System Poster
Solar System Poster


This is the Solar System´s smallest planet, moves from the morning sky to evening sky several times a year. As it never strays far from the Sun, it can be hard to find in the Sun´s glare.


The dazzling morning or evening star, outshines all the other stars and planets in the night sky.


The Red Planet, brightens during January and February until reaching its bi-annual opposition on 3rd March. Thereafter, it starts to fade until lost from view in October. It re-emerges from the Sun´s glare at the end of November, low in the south-west in the early evening.