Rotation and Revolution of the Earth

Rotation of the Earth:

• The spinning of the earth around its axis is called the rotation of the earth.
• The axis is the imaginary line passing through the centre of the earth.
• The earth completes one rotation in 23 hours, 56 minutes and 4.09 seconds.
• It rotates in an eastward direction opposite to the apparent movement of the sun (from west to east).
• The earth’s axis is inclined at an angle of 66½° to the orbital plane as it moves around the sun.
• the earth’s axis is tilted at an angle of 23½° from a perpendicular to the elliptic plane.
• The rotational velocity decreases from equator to pole and at the poles is nearly zero.
• The greatest velocity of the rotation is found at the equator. The velocity of rotation at the equator is 1,670 km per hour and in the poles, it is about zero.

 

Causes of Earth’s Rotation:

The rotation of the earth causes the following effects:

1. The apparent rising and setting of the Sun is actually caused by the earth’s rotation.

2. The alternate occurrence of day and night everywhere on the Earth’s surface.

3. Rotation of the earth is also responsible for the difference in time between different places on the earth.

4. A 24-hour period divided by 360 degrees gives a difference of 4 minutes for every degree of longitude that passes the sun. The hour (60 minutes) is thus 1/24 of a day.

 5. The earth rotates from west to east, the sun, moon, planets and stars appear to rise in the east and set in the west.

6. Rotation causes the working of the Coriolis force which results in the deflection of the winds and the ocean currents from their normal path.

7. Tide is caused by the rotation of the earth apart from the gravitational pull of the sun and the moon.

8. Rotation causes a flattening of Earth at the two poles and bulging at the Equator. Hence, there is a difference in diameter at the poles and equator.

 

Revolution of the Earth:

The movement of the earth in its orbit around the Sun in an anti-clockwise direction, that is, from west to east is called revolution of the earth.

• The earth revolves in an orbit at an average distance of 150 million km.
• The distance of the earth from Sun varies time to time due to the elliptical shape of the orbit.
• Perihelion (‘peri’ means close to and Helios means sun): About January 3rd the earth is closest to the sun. At Perihelion, the distance is 147 million km.
• Aphelion (Ap means away and Helios means sun): Around July 4th the earth is farthest from the sun. At Aphelion the distance of the earth is 152 million km away from the sun.
• The period taken by the earth to complete one revolution around the sun is 365 days and 6 hours (5 hours, 48 minutes and 45 seconds) or 365¼ days.
• The speed of the revolution is 1,07,000 km per hour. The speed is 30 km per second.

 

Period of Revolution and Leap Year:

The period of time the earth takes to make one revolution around the sun determines the length of one year.

The earth takes 365 days and 6 hours to complete one revolution. Earth takes 365.25 days to complete one trip around the Sun.

That extra quarter of a day presents a challenge to our calendar system, which has one year as 365 days.

To keep our yearly calendars consistent with our orbit around the Sun once in, every four years we add one day.

The extra day added to is called a leap day, and the year the extra day is added to is called a leap year.

The extra day is added to the month of February which has 29 days in a leap year.

 

Causes of Revolution of the Earth:

The revolution of the earth around the Sun results in the following

• Cycle of seasons,

• Variation in length of days and nights,

• Variation in distribution of solar energy over the earth and the temperature zones.

 

Difference between Rotation and Revolution:

Sr. No.	Rotation	Revolution
1.	Spinning of the earth from west to east on its axis.	Movement of the earth around the sun in its elliptical orbit.
2.	It takes 24 hours to complete a rotation (or a day)	It takes 365¼ days to complete one revolution (or a year)
3.	It is known as the daily or diurnal movement.	It is known as the annual movement of the earth.
4.	Rotation causes days and nights to alternate, tides, deflection of winds and ocean currents and also gives the earth its shape.	Revolution results in the varying lengths of day and night, changes in the altitude of the midday sun and change of seasons.

 

 

 Source: NCERT