Astronomy: Retrograde Motion Explained

Retrograde motion of the planets: Everything you need to know - BBC Science Focus Magazine

Mercury’s retrograde motion This video explains Mercury’s apparent retrograde motion in our skies: the inner planet appears to retrace its steps a few times per year. Every planet does this, every year. Retrograde motion is an optical illusion caused by differences in the planets’ orbital speeds. When a planet seems to reverse its direction in the sky, it’s called retrograde motion (from the Latin word retrogradus – "going backward"). Courtesy: Star Walk Based on video by James O'Donoghue / NASA

Why Mars Moves Backward - This is the retrograde motion of Mars. So why does Mars sometimes appear to move backward in the night sky? Retrograde motion is an optical illusion that happens when Earth, moving faster in its orbit, overtakes Mars. As we pass it, Mars appears to slow down, stop, and move westward temporarily — even though it's still moving forward in space. Because Mars orbits farther from the Sun than Earth does, it takes longer to complete one orbit. When Earth "laps" Mars about ev