Here's why:

* Earth's Rotation: Our planet spins on its axis, completing a full rotation roughly every 24 hours. This rotation is what causes day and night.

* Perspective: As the Earth rotates, different parts of the planet face the sun. We perceive this as the sun moving across the sky, even though it's actually the Earth that's moving.

* Apparent Path: The sun's apparent path across the sky varies depending on your location on Earth and the time of year. This is due to the Earth's tilt on its axis and its orbit around the sun.

It's important to remember that the sun itself is not actually moving across the sky. It's our perception of its position changing due to the Earth's rotation.