Instead of using a motion path for the moon's orbit you could just move the moon's center point from the center of the moon to the center of the Earth (select the moon, then press the insert key. The insert key will allow you to move the center point around by dragging it with the mouse) You could then point constrain the moon to the Earth. Now, all you have to do is write a simple expression to rotate the moon "moon.rotateY = time * 2" . Increase or decrease the number to make the moon rotate faster or slower.