The Sun doesn't actually move across the sky. It's the Earth that's rotating on its axis.

Here's why it looks like the Sun is moving:

* Earth's Rotation: The Earth spins on its axis, making one complete rotation every 24 hours. This is what causes day and night. As the Earth rotates, it seems like the Sun is moving across the sky because our perspective is changing.

* Earth's Tilt: The Earth is tilted on its axis at an angle of 23.5 degrees. This tilt causes different parts of the Earth to receive varying amounts of sunlight throughout the year. This is why we have seasons.

Think of it like this: imagine you are sitting on a spinning merry-go-round. As the merry-go-round spins, the trees and buildings around you seem to be moving, even though you know they are stationary.

So, the Sun appears to move across the sky because of the Earth's rotation.