The Sun doesn't actually move across the sky. It's the Earth's rotation that makes it appear to move from east to west.

Here's why:

* Earth's Rotation: Our planet spins on its axis, completing a full rotation roughly every 24 hours. This rotation causes the apparent movement of the Sun across the sky.

* Perspective: As Earth rotates, we see the Sun rise in the east, reach its highest point in the sky at noon (local time), and then set in the west.

Important Note: The Sun's position in the sky also changes throughout the year due to the Earth's tilted axis and its orbit around the Sun.