Here's why:

* Planets orbit the Sun: Planets, including Earth, move in orbits around the Sun.

* Earth's perspective: From our vantage point on Earth, we see planets against the backdrop of distant stars. As Earth orbits the Sun, our perspective shifts, causing some planets to appear to move "backwards" in a phenomenon called retrograde motion.

* Apparent motion: This backwards motion is an illusion. The planets are actually moving in their own orbits around the Sun, but their apparent motion from Earth can create the illusion of retrograde motion.

Let me know if you'd like a more detailed explanation of retrograde motion!