Till a few hundred years ago, it was believed that the Earth was the centre of the universe and that the Sun, the Moon and the stars revolved round it. This belief was based on the assumption that the Earth appears to be stationary, while the positions of the stars keep on changing. In 1545, Nicholas Copernicus, a Polish astronomer suggested that the Earth revolves around the Sun and completes one revolution in 365¼ days. This period is called a year. Secondly, it also rotates on its own axis and takes 24 hours to complete one rotation. If the Earth is rotating and revolving at the same time, why don’t we feel its motion? The answer is that because of gravity, all the things situated on the Earth including the atmosphere move with the Earth and hence we cannot feel its motion. If you rotate a football with an ant on it, the ant will not feel that the ball is rotating. Exactly like the ant on the football, we are present on the surface of the Earth and do not feel its movement. The biggest proof of the Earth’s motion is the change in seasons. Seasons occur due to the Earth’s revolution around the Sun as well as due to its rotation on its own axis. Day and night are caused by the Earth’s rotation on its axis. The portion of the Earth which faces the Sun experiences day, while the darker portion has night. If the Earth did not rotate on its axis, the part of the Earth facing the Sun would always have day while the rest would have night forever. The Earth’s axis makes an angle of 23½° with the vertical. As a result of this, one pole faces the Sun continuously for six months, and for the next six months, it does not. This explains the six-month duration of days and nights on the poles. All these observations confirm the motion of the Earth round the Sun, as well as on its own axis.