The motion of the Earth that causes day and night is rotation.

Here's how it works:

* Earth spins on its axis: The Earth rotates on its axis, an imaginary line passing through the North and South poles.

* One full rotation takes about 24 hours: This rotation takes approximately 24 hours to complete.

* Different sides face the sun: As the Earth spins, different parts of the planet face the sun. The side facing the sun experiences daylight, while the side facing away from the sun experiences night.

So, it's the Earth's rotation that causes the cycle of day and night.