Define Retrograde Motion.

Retrograde motion refers to the apparent backward or opposite movement of a celestial body, typically a planet, against the backdrop of fixed stars in the night sky. While planets orbit the Sun in relatively consistent directions, the combined effect of Earth's and a planet's orbital motion can create an illusion of temporary reversal in the planet's path, giving rise to retrograde motion.

From the perspective of an observer on Earth, as our planet overtakes and passes an outer planet in its orbit, the outer planet appears to move backward in the sky before resuming its usual forward or prograde motion. This phenomenon is particularly noticeable with planets that orbit the Sun beyond Earth's orbit, such as Mars, Jupiter, and Saturn.

Retrograde motion occurs due to differences in orbital periods and distances from the Sun. As Earth orbits at a faster speed and on a shorter path, it occasionally catches up with and overtakes outer planets, leading to the observed backward motion. This apparent reversal is a consequence of the relative positions and motions of the Earth and the outer planet in their respective orbits and is a recurring and predictable phenomenon in observational astronomy.