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Motions of the Earth

CHAPTER 2

 MOTIONS OF THE EARTH

REVOLUTION OF THE EARTH

It is earth’s motion in its elliptical orbit around the sun. One revolution is completed in 365 1/4 days, resulting in one extra day every fourth year. The year consisting of 366 days is called the ‘leap year’ having 29 days in the month of February. Effects of the Revolution of the Earth are as follows:

Motions of the Earth - Physical Geography, UPSC, IAS. | Geography (Prelims) by Valor Academy
Change of seasons.
Variation in the length of day and night at different times of the year.
Shifting of wind belts.
The earth’s axis is tilled at an angle of 23.5° from a perpendicular to the orbital plane.
In other words, the earth’s axis makes an angle of 66.5° with the plane of the earth’s orbit.

During one half of the year, the Northern Hemisphere and during the other half of the year the Southern Hemisphere is inclined towards the sun. Every point in the Hemisphere facing the sun takes a longer time to go out of the sunlight, with the result that the days are longer and nights shorter.

The Hemisphere Pole which is inclined towards the sun, the will have no night and the other Pole will have no day.
It is only on the equator that the day and the night are always of equal length.

Motions of the Earth - Physical Geography, UPSC, IAS. | Geography (Prelims) by Valor Academy

Revolution of the Earth and the Seasons

THE CYCLE OF SEASONS

On 21st June - North Pole is inclined towards the sun, while the South Pole is away from it. The rays of the sun are falling vertically not on the equator but on the Tropic of Cancer. In Northern Hemisphere the days are longer, nights shorter. It receives more heat than it loses. Therefore, it is having the summer season.

In Comparison, the rays of the sun are slanting in the Southern Hemisphere. Here is winter season in the Southern Hemisphere.

December  – It is the Southern Hemisphere which is inclined towards the sun while the

Northern Hemisphere is away from it. The vertical rays of the sun are now falling vertically on the Tropic of Capricorn. The days are longer and the nights are shorter in the Southern Hemisphere .It is therefore summer in the Southern Hemisphere and winter in the Northern Hemisphere.

23rd September and 21st March – The rays of the sun falls vertically on the equator at noon. Both the Poles receive the rays of the sun. As a result , exactly one-half portion of each Hemisphere receives the sun’s rays, making day and night equal all over the world on these two days.

On 23rd September it is the autumn season in the Northern Hemisphere and the Spring Season in the southern Hemisphere. The opposite is the case on 21st March.

ROTATION OF THE EARTH

The earth rotates around its axis. The axis is an imaginary line passing through the centre of the earth. The earth completes one rotation in 24 hours (23 hours, 56 minutes, 4.09 seconds to be exact).The earth rotates from west to east. Effects of the Rotation of the Earth are as follow:

Motions of the Earth - Physical Geography, UPSC, IAS. | Geography (Prelims) by Valor Academy

Causation of day and Night.

A difference of 1 hour between two meridians which are 15°apart. Defection of ocean currents and winds.

Rise and fall of tides every day. 

The document Motions of the Earth - Physical Geography, UPSC, IAS. | Geography (Prelims) by Valor Academy is a part of the UPSC Course Geography (Prelims) by Valor Academy.
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FAQs on Motions of the Earth - Physical Geography, UPSC, IAS. - Geography (Prelims) by Valor Academy

1. What are the different motions of the Earth?
Ans. The Earth has three main motions: rotation, revolution, and precession. Rotation refers to the Earth's spinning on its axis, which causes day and night. Revolution refers to the Earth's movement around the Sun, which causes the change of seasons. Precession is the slow change in the direction of the Earth's axis, which takes around 26,000 years to complete.
2. How does the rotation of the Earth affect day and night?
Ans. The rotation of the Earth causes day and night. As the Earth spins on its axis, different parts of the Earth receive sunlight, resulting in daytime. The areas facing away from the Sun experience darkness, leading to nighttime. This rotation takes approximately 24 hours, giving us a full day.
3. What is the significance of the Earth's revolution around the Sun?
Ans. The Earth's revolution around the Sun is significant as it causes the change of seasons. As the Earth orbits the Sun, different parts of the Earth receive varying amounts of sunlight throughout the year. This variation in sunlight leads to the four seasons: spring, summer, autumn, and winter.
4. How long does it take for the Earth to complete one revolution around the Sun?
Ans. The Earth takes approximately 365.25 days to complete one revolution around the Sun. This extra quarter day is why we have a leap year every four years, with an additional day in February.
5. What is precession and how does it impact the Earth?
Ans. Precession refers to the slow change in the direction of the Earth's axis. This means that over thousands of years, the orientation of the Earth's axis changes. As a result, the North Star, which is currently Polaris, will not always be the North Star. Precession does not have a significant impact on our day-to-day lives, but it does affect the Earth's climate over long periods of time.
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