Here's why:
* Earth's Rotation: Our planet spins on its axis, completing one full rotation every 24 hours. This rotation is what causes day and night.
* Perspective: As the Earth rotates, we on the surface see the Moon move across the sky. Because we're on a spinning sphere, the Moon appears to climb up from the eastern horizon and then descend towards the western horizon.
Important Note: The Moon's position in the sky is also affected by its orbit around the Earth. The Moon's orbit is tilted slightly, which is why we see different phases of the Moon and why the exact time and location of moonrise can vary.