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Rotation and Revolution are two main motions experienced by the earth. Rotation and revolution are important in space research. Rotation refers to the rotation of any planet to its own axis. While the rotation of one planet around another planet or object is known as revolution. The rotation of the Earth on its axis is from west to east, and the Sun and the Moon to move from east to west across the sky.
In case three-dimensional objects (such as the earth, moon and several other celestial planets) are rotating around an imaginary line, then it is known as the rotation axis. Celestial bodies always experience both rotation and revolution. Rotation can also be explained as a circular movement of an object around a centre of rotation. One revolution is when an object completes one full circle around its orbit.
Read More: Constellation
Key Terms: Rotation, Revolution, Rotation Axis, Center of Mass, Motion, Radius, Period, Axis, Ellipse
What is Rotation?
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Rotation is defined as the motion of any object around its own axis.
- Rotation is a circular motion in nature.
- There are many three-dimensional objects or planets such as the earth, moon, sun and more which rotate around an imaginary line that is known as a rotation axis.
- The rotation happens at an angle of –23.50 angle/tilt.
- When the axis passes through the centre of mass of the body then the body is said to rotate on its axis or spin.
Rotation Diagram
What are some of the examples of Rotation?Some of the important examples of rotation include:
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Rotation of Earth
Earth experiences rotational motion, which can be defined as:
- If the earth spins around its own axis, then it is called the rotation of the earth.
- Moreover, the rotation axis is perpendicular to the plane of the earth’s orbit.
- When the earth rotates, it tilts on the axis.
- Due to tilt, the earth divides into a lit-up half and a dark half which causes the rise of the day as well as night.
Facts about Rotation of Earth
There are some interesting facts about the rotation of the earth. Some of them include:
- Earth’s rotation or spinning happens on its axis at an angle of -23.5 degrees.
- Earth’s rotation causes day and night.
- The time taken by earth for one rotation is about 24 hours.
- Earth spins counter-wise.
Importance of Earth Rotation
The importance of earth rotation is as listed below:
- The Earth’s rotation forms the diurnal cycle of lightness and darkness.
- It also causes temperature and humidity changes.
- Earth’s rotation is the reason why tides in the oceans and seas occur.
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What is Revolution?
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Revolution is defined as the motion of any object or planet around the other object or planet.
- Revolution is an orbital motion in nature. Rotation and revolution are often assumed the same, but, revolution is an orbital revolution which is different from rotation.
- Moreover, the time taken by one object to complete one revolution is the circumference of that object. This duration of time is called a period.
- The revolution of the earth takes approximately one year (365 days) to complete one revolution.
Below is the diagram which shows how other objects revolve around the sun.
Revolution
What are some examples of Revolution?There are several examples of revolution. Some of them include:
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Revolution of the Earth
When the earth is moving around the sun in a fixed path it is called a revolution. Earth’s path revolves around the sun is known as orbit.In this, the earth is revolving around the sun in an oval shape which is known as an ellipse.
Facts about Revolution of the Earth
There are some interesting facts about the revolution of the earth which are mentioned below:
- Earth revolves in an oval shape which is called an ellipse.
- The time taken by the earth to complete one revolution around the sun is called a revolution or orbit.
- Time taken by earth for one revolution = 365.25 days or one year.
- The revolution speed of the earth is 68,000 miles per hour.
Importance of Revolution
Some of the many importance of revolution are:
- The change of seasons is caused by Revolution.
- Revolution forms “perihelion” and “aphelion”. Perihelion takes place when the Earth is closest to the Sun. Whereas, Aphelion happens when the Earth is away from the Sun.
- Revolution directly influences the variation of the length of day and night time. When the day and night duration are the same at the equator, it is called an equinox. While, when the day and night duration vary in the Northern and Southern hemispheres, it is called solstice.
Effects of Rotation and Revolution on Seasons
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There are four different seasons such as summer, winter, autumn and spring caused due to the rotation and revolution of the earth around the sun.
- Due to the rotation and revolution, there are several changes in the duration of the season.
- Also, temperature, as well as humidity changes occur due to the rotation of the earth.
- The shadows are also affected by rotation and revolution.
- Moreover, it is considered that the direction of earth rotation depends on the direction of viewing.
- Earth spins counterclockwise when viewed down from the north pole. On the other hand, the earth spins clockwise when viewed from the south pole.
Some important facts about the seasons on the earth are mentioned below:
- The revolution of the earth around the sun and the unchanging tilt of the earth’s axis cause the effect of seasons.
- When the north pole tilts towards the sun then the northern hemisphere experiences the summer season.
- When the south pole tilts towards the sun then the northern hemisphere experiences the winter season.
- In Summer, the sun is more overhead as well as direct towards the earth which causes a more direct or strong path for the radiation.
- In Winter, the sun is more slanted and indirect towards the earth which causes a less direct or weaker path for the radiation.
- In summer, shadows are shorter.
- In Winter, shadows are longer.
Difference between Rotation and Revolution
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Most of the time rotation and revolution are considered as the same thing. But, both are different scientifically, in astronomy, both the motions have their own definition and significance. On the basis of this, there are some main differences in rotation and revolution which are written below:
| Rotation | Revolution |
|---|---|
| Rotation is defined as the circular motion of one object around its own axis. | Revolution is defined as the circular motion of one object around the earth object. |
| The object or earth moves around the internal axis. | In revolution, the object moves around the external axis. |
| In rotation, the position of the object does not change. | In revolution, the position of the object changes with revolution. |
| Earth rotates from west to east. | In revolution, the earth revolves in a counterclockwise manner. |
| Earth’s rotation causes day and night. | Revolution of the earth causes seasons like winter, summer, spring and autumn. |
| Rotation located inside the body of the object | Revolution located outside the body of the object |
| The time taken by the earth to complete one rotation with respect to the sun is 24 hours | The time taken by the earth to complete one revolution around the sun is 365 days or complete one year. |
| In rotation, the earth is tilted at an angle of 23.5 degrees (23.50) | In revolution, the earth is referred to as an orbit which is elliptical. |
| Common Examples: Hand of clocks, the motion of wheels, motion of Ferris wheel in an amusement park, spinning top etc. | Common Examples: planets moving around the star, earth moving around the sun, electrons around the nucleus etc. |
Rotation and Revolution of Planets
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The period of rotation and revolution of planets with respect to the radius and distance in the form of a chart is shown below:
| Name of the Planet | Approximate radius(assuming radius of earth as 1 unit) | Approximate distance from the Sun (assuming distance of earth as 1 unit) | Period of Rotation | Period of Revolution |
|---|---|---|---|---|
| Mercury | 0.40 | 0.39 | 59 days | 88 days |
| Venus | 0.95 | 0.72 | 243 day | 225 days |
| Earth | 1.00 | 1.00 | 24 hours | 356.25 days |
| Mars | 0.55 | 1.50 | 24 hours 37 minutes | 687 days |
| Jupiter | 11.00 | 5.20 | 9 hours 55 minutes | 12 years |
| Saturn | 9.00 | 9.50 | 10.66 hours | 29.46 years |
| Uranus | 4.00 | 19.20 | 17.2 hours | 84 years |
| Neptune | 3.90 | 30.00 | 16.1 hours | 165 years |
Things to Remember
- In rotation, the body moves around its own axis.
- In revolution, the body moves around another body.
- The time taken by the rotation of the earth is 24 hours.
- The time taken by the earth for one revolution is approximately 365 days.
- In rotation, the earth tilts at an angle of 23.5 degrees.
- The revolution speed of the earth is around 68,000 miles per hour.
- The sun is more overhead the earth in the summer season which causes a direct path for the radiation.
- The sun is more slanted towards the earth in the winter season which causes an indirect path for the radiation.
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| Chapter Related Topics | ||
|---|---|---|
| Black Hole | Halleys Comet | Variable Star |
| Dark Side of the Moon | Life Cycle of Stars | Motion of Celestial Bodies in Space |
Sample Questions
Ques. What do you mean by Rotation? Also, write its measurement unit? [3 marks]
Ans. The movement of one object around its own axis is called rotation. Rotation plays a significant role in classical mechanics. Earth's rotation causes day and night. Rotational motion is present everywhere around us. Moreover, not only is rotation seen in astronomy but there are many things in our day-to-day life which perform the rotational motion. In Rotation, the earth moves around the north and south poles at an angle of 23.5 degrees.
For Example: Ferris wheel, spinning top, earth moves around its own axis, globe turns around its own axis, the motion of cricket ball etc.
The measurement unit of rotation is the radian.
Ques. What do you mean by Revolution? Also, write its measurement unit? [3 marks]
Ans. The circular motion of an object around another object is called revolution.In revolution, an object revolves around the external axis of the object. The time taken by one object to complete one revolution is the circumference of that object. This duration of time is called a period. Period is denoted as T. The revolution of the earth takes approximately one year(365 days) to complete one revolution. Also, in revolution, the position of objects changes.
The measurement unit of revolution is considered rotational speed which is measured as revolutions per minute(rpm), cycles per second (cps) etc.
Ques. What do you understand from the axis? [2 marks]
Ans. The imaginary line which passes through the object as well as also through the north and south poles is known as the axis or rotational axis. At the time of the earth’s rotation, the axis passes through the north and south poles and the earth tilts at an angle of -23.50 during the rotation. The figure below shows the axis in the earth:
Here, the dotted line indicates the axis. With the rotation axis, the earth makes an angle of 23.5 degrees.
Ques. Write down the key differences between rotation and revolution. [3 marks]
Ans. There are lots of differences between rotation and revolution. Here, we shall discuss some of the key differences in rotation and revolution:
| Factors | Rotation | Revolution |
|---|---|---|
| Definition | The movement of an object around its own axis is known as rotation | The movement of one object around the other object is known as revolution |
| Location of motion | In rotation, circular motion is located inside the body. | In revolution, circular motion is located outside of the body |
| Axis | The object or earth moves around the internal axis. | In revolution, the object moves around the external axis. |
| Position | In rotation, the position of an object is unchanged | In revolution, the position of objects changes. |
| Direction of motion | Earth’s rotation is from west to east. | In revolution, the earth revolves counterclockwise. |
| Time taken | In rotation, 24 hours is taken by earth to complete one rotation. | In revolution, approximately 365 days are taken by the earth to complete one revolution. |
| Examples | Spinning top, ferris wheel, earth’s rotation, globe turns around the axis etc. | Earth revolves around the sun, the moon revolves around the earth, electrons around the nucleus etc. |
Ques. What do you understand from Equinox? [2 marks]
Ans. Equinox is a special phenomenon which describes the equal duration of days and nights on the earth. At the equatorial point, the equator of the earth passes through the geometric centre of the sun’s disk. Also, the centre of the visible sun is directly above the equator. During this time period, the length of the day and night are equal. This moment occurs only twice a year, that is 22 September and 20 March.
Ques. Can the rotation of earth be slowed down artificially? [3 marks]
Ans. After much research done by scientists, it is considered that artificial methods of slowing down the rotation of the earth do not put much impact on the rotation of earth. Also, it is considered that humans have made some measurable variation in the rotation period of the earth by several milliseconds by collecting trillions of tons of freshwater into the vast reservoirs. This usually happens in the equatorial temperature zone. There is a weak interaction between this activity and weather over the long term. Also, it is considered that the strength of the magnetic field of the earth is very sensitive to the rate of the earth’s rotation.
Ques. Do all the stars in the sky move? [2 marks]
Ans. No, all the stars do not move in space or the sky. Only the pole star which is located above at the axis of rotation of the earth in the direction of the north occupied the fixed position. Except for the pole star, other stars seem to move in the sky.
Ques. What is a constellation? Name any of two constellations. [2 marks]
Ans. Constellation refers to the group of stars which form a specific pattern or shape. The constellation contains a large number of stars. Some of the stars are bright while some are dim. The bright stars can be seen easily with our naked eyes while it is quite difficult to see dim stars. Two main constellations' names are as follows:
- Aries
- Ursa Major
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