Earth's Two Motions: Rotation and Revolution
Earth's Two Motions: Rotation and Revolution As a planet of the sun, the Earth revolves around the sun. Besides this, it also rotates on its own axis. Thus the Earth has two motions: the rotation and the revolution. Rotation The Earth rotates on its axis from west to east. The axis is an imaginary line passing through the northern and the southern poles. Earth's rotation is completed in about 24 hours — this is called the daily motion of the earth. This motion is responsible for the occurrence of day and night. One rotation is completed when a given heavenly body crosses the observer's meridian two times in succession. How rotation periods are calculated: The period of rotation is calculated with reference to a star and with reference to the sun. When it is calculated with reference to a star, it is called a sidereal day and when it is calculated with reference to the sun, it is called a solar day. Solar days and sidereal days: ...