The cycle of the day and night is a result of earths spinning on its axis, which is earths

Axis an imaginary line about which the earth rotates.

Explanation: The change in day and night is due the rotation of the earth on its axis. A solar day, 24 hours, is the time taken by the earth to rotate once so that sun appears at the same place next day. But the real time of rotation of the earth is less, 23 hours 56 minutes and 4 seconds. It was Discovered by observing the time taken by a star to appear next day at the same place in the sky and this is called sidereal day.

The axis is the imaginary line that goes through its center.

As Earth rotates on its axis there are certain times when areas of Earth are not facing the Sun. The result is night.