The definition of the earth's rotation:

The earth rotates around its axis of rotation from west to east, counterclockwise from the North Pole and clockwise from the South Pole. All kinds of theories about the earth's rotation are still hypotheses at present.

Earth rotation speed:

The rotation of the earth is an important movement form of the earth. The average rotation angular velocity is 4. 167× 10 (-3) degrees/second, and the rotation linear velocity on the equator of the earth is 465 meters/second. It takes 23 hours and 56 minutes for the earth to rotate once, increasing or decreasing by three thousandths to four thousandths of a second every 10 year.

The earth's rotation speed, which has been slowing down for a long time, began to accelerate from 1999. NIST timekeepers said that in order to adjust the Earth's time and atomic clock according to the Earth's rotation speed, the Earth's standard clock increased by **22 leap second time during the 27 years from 1972 to 1999, but leap second was not added after 1999, and the Earth's rotation speed was accelerated.

The significance of the earth's rotation:

1, alternating day and night:

Because the earth is a sphere that is neither luminous nor transparent, the sun can only illuminate half of the earth's surface at the same time. The hemisphere facing away from the sun is daytime, and the hemisphere facing away from the sun is night.

Because the earth keeps rotating and alternating day and night, the cycle of day and night alternation is 1 solar day. The alternation of day and night affects people's daily life, so the solar day is the basic unit of time.

2. The horizontal movement direction of the deflection object:

The force that deflects an object in the direction of horizontal motion is called geostrophic deflection force. The geostrophic deflection force only acts on the horizontally moving object, always perpendicular to the horizontal conveying direction of the object, and increases with the increase of the horizontal conveying speed of the object.

In the northern hemisphere, it points to the right of the direction of motion; In the southern ball, it points to the left in the direction of motion. Objects moving along the equator are not affected by the geostrophic deflection force.

3. Time difference:

Local time: When the time when the sun rises to the highest in a place is noon 12, the time between two consecutive 12 hours is divided into 24 hours, and the time system thus formed is called local time.