Here's why:

* Earth's Rotation: The Earth spins on its axis, completing one full rotation approximately every 24 hours. This rotation is what causes day and night.

* Our Perspective: As the Earth rotates, different parts of the planet face the sun. We, as observers on Earth, perceive this change in facing direction as the sun moving across the sky.

* The Illusion: The sun itself isn't actually moving; it's our planet's movement that creates the illusion of the sun's motion.

Think of it like this: Imagine you're on a carousel. As the carousel spins, the scenery around you seems to be moving, even though you're the one rotating. The same principle applies to the Earth's rotation and the apparent movement of the sun.