Motion of the Earth
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 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.
FAQs on Story of Motions of the Earth
1. What are the two primary motions of the Earth as explained in the NCERT syllabus?
The two primary motions of the Earth are rotation and revolution. Rotation refers to the spinning of the Earth on its axis, which takes about 24 hours and causes day and night. Revolution is the Earth's movement in a fixed orbit around the Sun, which takes approximately 365.25 days to complete and is responsible for the changing seasons.
2. What are the main effects of the Earth's rotation?
The most significant effect of the Earth's rotation is the cycle of day and night. Other important effects include:
The creation of a 24-hour day.
The apparent movement of the Sun, Moon, and stars across the sky.
The influence on the direction of wind and ocean currents, known as the Coriolis effect.
The daily occurrence of high and low tides.
3. What is the difference between a solstice and an equinox?
The key difference relates to the position of the Sun relative to the Earth's equator and the resulting length of day and night.
A solstice marks the point when the Sun is farthest from the celestial equator, leading to the longest day (summer solstice) or the shortest day (winter solstice) of the year.
An equinox occurs when the Sun crosses the celestial equator, resulting in nearly equal lengths of day and night across the entire world.
4. Why do we have a leap year every four years?
A leap year is necessary because the Earth takes approximately 365.25 days to complete one revolution around the Sun. Our standard calendar year is 365 days. The extra 0.25 day (or 6 hours) accumulates over four years to become a full day. To keep the calendar aligned with the Earth's orbit, this extra day is added to the month of February every four years, creating a leap year with 366 days.
5. How does the Earth's revolution cause the change of seasons?
The change of seasons is caused by the combination of the Earth's revolution and its 23.5-degree axial tilt. As the Earth orbits the Sun, this tilt causes different hemispheres to receive more direct sunlight. When the Northern Hemisphere is tilted towards the Sun, it experiences summer, while the Southern Hemisphere has winter. Six months later, the situation is reversed. The seasons are a result of this changing angle of sunlight, not the Earth's distance from the Sun.
6. What would happen if the Earth's axis was not tilted?
If the Earth's axis had no tilt (a tilt of 0 degrees), life on our planet would be dramatically different. There would be no seasons. The climate at any given location would stay the same all year round. Furthermore, every place on Earth would experience approximately 12 hours of daylight and 12 hours of darkness every single day. The Sun's direct rays would always be focused on the equator.
7. What is the circle of illumination and how is it related to day and night?
The circle of illumination is the imaginary line that divides the Earth into a sunlit hemisphere (day) and a dark hemisphere (night). As the Earth rotates on its axis, different parts of the planet continuously pass through this line, causing the transition from day to night (sunset) and from night to day (sunrise). The circle of illumination does not align with the Earth's axis due to the planet's tilt.
8. Why are days and nights longer or shorter at different times of the year?
The variation in the length of days and nights is due to the Earth's axial tilt. During summer in a particular hemisphere, that hemisphere is tilted towards the Sun. This means a larger portion of it stays in the sunlit part of the Earth during one 24-hour rotation, resulting in longer days and shorter nights. In winter, the same hemisphere is tilted away from the Sun, so it spends less time in the sunlight, leading to shorter days and longer nights.
