How Fast Does The Earth Rotate On Its Own Axis?
The planets that revolve around the Sun also spin on their axis in a process known as rotation. The period a planet uses to complete a rotation varies, and the longest rotation period of any planet in the Solar System being that of Venus. The Earth rotates eastwards on its axis which is located on the Geographic South Pole and the North Pole. The Earth uses 24 hours to complete one rotation in relative to the sun.
Origin Of The Rotation Of The Earth
Astronomers believe that the Earth has been spinning on its axis since its formation several billions of years ago. Using the giant-impact theory, the Earth’s rotation is believed to have been accelerated greatly during the formation of the moon after the collision of a major celestial body with the Earth which led to the formation of the moon. Scientists estimate that the Earth might have completed one rotation in only five hours immediately after the giant impact. However, tidal effects are believed to have gradually slowed down the rotation.
True Solar Day
A true solar day is a period the Earth takes to complete a full rotation relative to the Sun. The true solar day is variable and changes from time to time. The changes are based on the inclination of the Earth. The period is longer near the perihelion than near the aphelion.
Mean Solar Day
The mean solar day is the average of the total actual solar days in a year where the average solar day is made up of 86,400 mean solar seconds. There is a variation in mean solar day and it is longer than it was in the past centuries as a result of the effects of tidal friction. The mean solar second is established as the SI second used to measure the speed of the rotating Earth.
Changes In Rotation Of The Earth
The rotation of the Earth has been constantly changing through the course of its history. These changes either affect the rotational axis of the Earth or the rotational velocity of the Earth. The Earth’s rotational axis is primarily affected by external torques emanating from the gravity of other celestial objects such as the Sun and the Moon. The changes in the Earth’s rotational axis are based on the Earth’s position with respect to inertial space as well as the Earth’s crust. Changes in the Earth’s rotational velocity are caused by several factors which are either terrestrial or extraterrestrial. Some terrestrial events have been observed to have an effect on the Earth’s rotational velocity with one example being the 2004 Indian Ocean Earthquake which increased the rotational velocity by about three milliseconds. The ongoing post-glacial rebound is also affecting the rotational velocity by shifting the Earth’s mass. One extraterrestrial factor which has affected the Earth’s rotational velocity is the moon through tidal interactions between the two celestial bodies. The moon has been moving away from the Earth since its formations millions of years ago and therefore the impact of its gravity has been gradually receding throughout its history. Scientists believe that a true solar day lasted 21 hours about 600 million years ago.
The ancient Babylonians and Chinese astronomers kept records of key astronomical events such as lunar eclipses and solar eclipses. The medieval Islamic astronomers also kept records of such events. Modern astronomers can use these records which date back thousands of years to calculate and establish the changes in the Earth’s rotation for the past 2,700 years.