The Rotational Movement of the Sun

Day and night are caused by the movement of the sun that is known as Rotational Movement. 

Earth's Day and Night. Another effect of Earth's rotation is that we have a cycle of daylight and darkness approximately every 24 hours. This is called a day. As Earth rotates, the side of Earth facing the Sun experiences daylight, and the opposite side (facing away from the Sun) experiences darkness or nighttime.