NCERT Class 6 Geography Chapter 3: Motions of the Earth Complete Notes Part 3

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Motions of the Earth

What Would Happen if Earth Does Not Rotate?

Image of Unerstand for Frozen and Extreme warmth

Image of Unerstand for Frozen and Extreme Warmth

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So that is important to understand like you have sun which is coming from here and what would happen if the earth does not rotate? If earth does not rotate and this part is facing the sun always what would happen? This side would be always day and other side would be always night. In other words I would say this side to be extremely warm. However the other side becomes extremely cool and it would be kind of frozen. So would who happen if this is not rotating? If this does not rotate, it would move this face again. When taking revolution the same thing would happen, this would face the sun and it would be day and warm, and other side again would be darkness and frozen cold.

Now this two for the general phenomena the earth motion we are familiar with, there is third phenomena that we understand that is a precession.

Axial Precession – 26,000 Years – Changes North Star (Polaris to Vegas)

Image of Axial Precession

Image of Axial Precession

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Now understand precession you must be very clear cut idea that should form background for precession. First of all let’s consider earth here, what would happen if I am seeing the earth from point in space which is at top, so I’m looking down on the earth from point in space. What would happen? This earth would appear to move counter clockwise to the sun. When I am outside the earth at a point in space. If I am outside the earth looking straight forward to the earth what would happen? It would look as if it is spinning east west. So when I say spinning east west what would happen when I am on the earth standing on the earth I see the sky moving. I see everything moving east to west that is because we consider the movement from east to west so everything in the sky be it sun, be it moon appear to move westwards. When I am standing on the earth now understand then there was idea that was laid down back the time of Greeks and that was mainly forwarded by Hipparchus. He was Greek astronomer and geologist and he tried to explain that there is third phenomena that exist and this phenomena is known as precession. Now whenever there is precession that occurs, its important to understand that there is movement of the earth which is beyond rotation and revolution and which is of kind of spinning of a top .

So when you have top that is spinning it would have circular motion and that circular motion would continue for some time and ultimately this would vibrate or move down and that is vibrating movement. So if I say I have a pen and that is moving this way. It would be a kind of precession movement and that precession movement. It is explain here now in this precession when we talk about this we have axis of the earth and axis of the earth there is precession along the axis of earth that takes 26,000 year to complete. Now this animation is bit diverted from the scale the rotation of the earth should be very fast because a taking every day for 26,000 year, it should very fast and in degree it moves 72 years as per precession of the year. Now why this precession? It is mainly to due to now uniform gravitational pull that exist between sun and the moon.

Now I represent we explain Polaris is a north star when after 13,000 year a north star would change to Vegas and again by 28,000 AD we would say north star is back to Polaris, in between you would have 23,000 years. We would say the north star to vary and because of precession when we talk about precession there are two types of precession that we must be understand. First is Axial Precession and second is orbital precession. Now axial precession is completed in 26,000 years and there was an another way try to explain the axial precession.

Image of Axial Precession for example

Image of Axial Precession for Example

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Precession of equinox and this is due to some theory which are given and some binary star theory or dual model theory. It was considered as entire solar system that moves around some point in the space that means that sun is also in movement along common center star or another star would say is a binary star or dual star and the entire solar system is moving. As a result we consider 12 constellations every month and that we try to explain this is because of axial precession of the earth that takes place and that called as a precession of equinox. When were try to explain how there is change in a constellations that is place and North Star changes with time. So Vegas would be in different constellation, Polaris would be different constellation by around 75,000 AD.

That means you would have different constellation that would happen with change in the axial precession that would occur.