Story of Motions of the Earth

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Motion of the Earth

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Earth as we know Is the 3rd planet in the solar system. The solar system is a system of planets wherein all the planets, 8 to be precise revolve around the giant ball of fire, the sun. All these 8 planets revolve around the sun in an orderly manner and always follow the same trajectory. The trajectory or path followed by every planet is known as its orbit. Every planet has a different orbit. These orbits aren't circular in shape, in fact, they are elliptical. The radius of orbits varies and the increase in the radius results in the arrangement of the planets in an orderly manner. 

What are the Two Motions of the Earth? 

As we just learned, every planet revolves around the sun in a specific orbit. So does our planet. Our planet revolves around the sun with a period of 365.25 days. Likewise, every other planet has a time period of its own, this time period increases as the distance from the sun increases. Revolution, however, is just one of the motions executed by our planet, earth. Our planet also rotates on its own imaginary axis. Both of these motions happen together, the earth revolves and rotates simultaneously. 

Rotation of the Earth

The earth rotates about its tilted imaginary axis from West to east. The time period for this rotation is 24 hours. That means the earth completes one full rotation after every 24 hours. So your net displacement after 24 hours will be 0. If viewed from the pole star, the earth appears to rotate counterclockwise. 

Some History About the Discovery of Rotation of Earth

Some of the scholars in 470 BC believed that the rotation of the earth is just an apparent thing and in reality is just an illusion. However, it was for the first time in 499 BC, Aryabhatta, an Indian scientist stated that the earth rotates about a fixed axis daily. Soon the statement spread to the west and western philosophers started believing that the earth does rotate about a fixed axis. 

Revolution of Earth Around the Sun 

Revolution is the second phenomenon executed by the earth. The earth goes around the sun in an elliptical orbit every 365.25 days, this periodic motion of the earth is called a revolution. The earth's orbit is an eclipse and the earth-sun barycenter is one of the focuses of this ellipse. The eccentricity of the ellipse is 0.0167. Ever wondered why the earth revolves around the sun? Well, if not then let's find the answer out today! 

Why Does the Earth Revolve Around the Sun? 

Why does the earth have to revolve around the sun? Well, this is because the sun has a huge mass. It's a lot greater than the mass of earth or any other planet in the solar system. Sun is the biggest body in our solar system and hence it has the highest gravitational force. Gravitational force is the force between two bodies that is dependent on the masses of both bodies. The higher is the mass, the stronger is the gravitational pull. Hence, the sun being the heaviest controls the motion of all the other planets in the solar system. 

Some Numbers That Will Take You By Surprise! 

The average distance travelled by the earth 

149.60 million kilometres

The time period of revolution

365.256 days 

The eccentricity of the orbit of the earth


Earth's orbital speed 

29.78 Km/second 

The History Behind the Discovery of Revolution

Heliocentrism is the first-ever model which was designed according to the theory which said that the sun is at the center of the solar system. Until then, the theory of geocentrism was believed according to which the earth was the center of the solar system. Soon Copernicus came up with his theory of a static center, that is the sun. And all the planets moved around this static center In fixed orbits. Then, experiments were conducted to prove the theory and soon the world started believing the theory of heliocentrism. 

Fun Fact: 

The earth's rotation period is reducing with each passing day. This means that days in the past were longer than days today. Well, this isn't just a joke and has scientific backing to it. The earth's rotation period is known to be decreasing as we progress forward in time. This is due to the moon's tidal effect. According to some experiments conducted by a few learned scientists, a day today is almost 1.7 milliseconds lesser than a day, one century ago. Although, the time lag is not much, with time this shall definitely increase. 

FAQ (Frequently Asked Questions)

1. What is the Influence of Rotation on the Earth?

The two motions of the earth have a huge influence on earth, rotation is the major cause for the existence of a day and night. As the earth rotates, every part of the earth is exposed to the sun one by one. This in turn embarks the separation between day and night. The side facing the sun would experience day whereas the side which is away from the sun would experience night. Hence, we have a huge time difference between India and America. Apart from this rotation is also responsible for the tidal effects generated due to the moon's gravitational force. 

2. What is the Effect of the Revolution on the Earth?

Both the earth's motions have a huge impact on the earth. Just like rotation, the revolution also has a huge impact on the phenomenons observed on the earth. One revolution demarks the completion of one whole year. The time period of the sun is 365.25 days and hence, every 4 years this quarter-day adds up and causes a leap year. Revolution of the earth around the sun is also the reason behind the change of season. The earth's orbit is an ellipse and the sun is at one of the focus. Hence when the earth is away from the sun, i.e. closer to the other focus, it is winter season on earth whereas when the earth is near the sun, the earth experiences summer.