The Earth spins on its axis from west to east at a speed of 1670 km per hour near the equator. This spinning of the Earth on its axis is called 'Rotation'. The Earth takes 23 hours 56 minutes and 4 seconds, or a day, to complete a rotation on its axis, which causes day and night in the Earth. Since the Earth completes its rotation in a day, rotation is also known as the 'Daily Movement of the Earth'.
The Earth rotates from west to east. That is why, if a stone is dropped from the top of a high-rise building or a tower, it will fall slightly toward the east. It also determines the direction in which the Sun, the Moon and the Stars rise and set.
During rotation the surface of the Earth that faces the Sun has day, while the other part has night. This occurs because the Earth is shaped like a ball or sphere and the Sun cannot light up the whole sphere at the same time. When one Hemisphere or half of the sphere faces the Sun, the other half is turned away from the Sun. Thus the half that faces the Sun has day, while the other half gets no light at that time and has night. As the Earth rotates, the sunlit side gradually moves away from the Sun into darkness at sunset and the side that was away from the Sun and had darkness gradually moves into daylight at sunrise. Thus, all the places on the Earthâ€™s surface continuously get periods of daylight, followed by periods of darkness or night.
A faint light, known as 'Twilight', illuminates the Earth, before sunrise and sunset. Twilight occurs due to the reflection of the sunlight from the upper layers of the atmosphere on the Earth, while the Sun is below the horizon.
The circular boundary between the illuminated or sunlit part of the sphere and the part in darkness is called 'Shadow Circle' or the 'Circle of Illumination'.
Rotation therefore causes day and night. The change of day to night in its turn causes variation in temperature. During the day the heat of the Sun raises the temperature, while at night, the accumulated heat is radiated into the atmosphere and the temperature comes down. Since the Earth rotates from west to east, it seems to us that the Sun makes its journey from east to west. Similarly, a person sitting inside a moving train, finds that everything outside - the trees, the fields, the hills, the houses - are moving backwards.