Planets don't actually change their direction of movement in the night sky. The apparent retrograde motion is an illusion created by the relative motion of Earth and the planet as they orbit the Sun. Here's a breakdown:

1. Earth and Planets Orbit the Sun: Both Earth and other planets in our solar system orbit the Sun in the same direction, but at different speeds.

2. Earth's Faster Orbit: Earth orbits the Sun faster than the outer planets, like Mars.

3. The Illusion: When Earth overtakes an outer planet in its orbit, from our perspective on Earth, it appears as if the outer planet is temporarily moving backwards in the night sky. This is because we are catching up to it, changing our relative position.

Imagine this: You're driving on a highway and pass a slower car. From your perspective, it seems like the slower car is moving backwards momentarily, even though it's still traveling in the same direction. Retrograde motion is similar.

Here's a visual:

* Direct Motion: A planet typically moves eastwards across the night sky (from our perspective).

* Retrograde Motion: When Earth overtakes the planet, it appears to move westwards for a short period.

Important Note: Retrograde motion is not a change in the planet's actual orbit. It's simply a visual effect caused by our changing viewpoint as Earth orbits the Sun.