Chapter 2 Shape Of The Earth Is The Earth Round? Introduction :

Like the origin of the Earth, the subject of the shape of the Earth was for a long time a matter of great speculation. In ancient times ‘people had a lot of confusion about the shape of the Earth.

Some said the Earth was a plane, some said flat,  etc. Later it was learned that it was neither plane or flat but a sphere. To prove it is a sphere, many examples, evidence, and experiments were given.

But to know the actual shape of the Earth today, these experiments or evidence are not necessary. Now, daily photos are taken by space crafts or satellites allow us to understand the actual shape of the Earth.

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Impression Of The Ancient People About The Shape Of The Earth :

In ancient times, the Earth was considered to be a flat disc with steep edges. Aryabhatta, the famous Indian astronomer, however, believed that the Earth was spherical in shape and rotated on its axis.

In Europe, the Greek philosopher Pythagoras was the first that the Earth was spherical in shape. The Hebrews and the Babylonians regarded the Earth as circular in shape circumscribed by a river Okeanos.

They imagined the sky and the firmament as a dome-shaped casket from the windows of which rain fall. The Greek philosophers soon realized that the Earth was a sphere and it was first Aristotle and then Copernicus, who declared the Earth is as round as a ball.

Later on, came Sir Isaac Newton who asserted that the Earth is not a complete ball but an oblate spheroid. Since the eighteenth-century people have to give analogies about the shape of the Earth.

Some scientists have called it orange-shaped while others have compared to a pear. A few have called it a ‘tetrahedron’.

Who First Noticed And Claimed That The Earth Is Round?

Aristotle, a Greek Philosopher and scientist was the first person who observed the circular shadow of the Earth on the moon during a lunar eclipse and concluded that the Earth is round.

Around 350 B.C. he declared that the Earth was round. Aryabhatta, the ancient Indian scientist and Greek geographer Eratosthenes endorsed the idea of a round Earth.

Why We Do Not Feel That The Earth Is Round?

If an arc has a smaller radius, more is its curvature, and if the radius of an arc is less is its curvature.

The Earth is so big with great dimensions, a little part of its we can see at a glance. The mean diameter of the Earth is about 12734-5 km, while its mean radius is about 6368 km (6400 km).

 

 

 

 

When we stand on the surface of the Earth we can actually get to see a very small portion of the Earth and it seems to be flat to us.

A few practical observations or proofs in support to the round/spherical shape of the Earth :

The fact that the Earth is spherical in shape is based on the following phenomena.

(1) Shadow Of The Earth :

At the time of the lunar eclipse the shadow of the Earth falls on the Moon is spherical. It can be proved with the help of geometry that only a sphere will cost a circular shadow on a flat surface. Hence, as the Earth is a sphere, its shadow is also spherical.

 

 

 

(2) Shape Of Other Planets Of The Sun :

All planets of the Solar System are spherical in shape as seen through the telescope. The Earth is also a planet of the Solar System, so its shape will also be spherical which is logical.

 

 

 

 

(3) Sunrise And Sunset :

If the Earth was flat, Sunrise and Sunset would occur at the same time at all places. But we know countries located in the east have Sunrise and Sunset earlier than countries lying to the west.

(4) Position Of The North Pole Star :

The Pole star which appears overhead at the North Pole when seen from any place proves that Earth is a spherical shape.

(5) Effect Of Gravity :

Gravity—whose effect is nearly equal to all the places on the Earth is another proof that Earth is a sphere.

(6) The Spherical Horizon :

The limit of the horizon at a place is circular and the horizon widens as the height of the observer increases. This again indicates the spherical shape of the Earth.

(7) Sighting A Ship :

As one observes a ship coming towards a port, the smoke is first noted. Later the funnel and mast of the ship are seen and finally, the hull of the ship comes into view.

This shows that the sea level has a curved surface. If the Earth was a flat disc, the entire ship would be seen even from a distance.

(8) Circumnavigation :

As the Earth is spherical in shape, it is possible to circumnavigate the Earth. Magellan was the first to go round the Earth in a ship and complete his voyage without encountering a sharp edge.

Now aircraft make many trips around the world on scheduled flights.

(9) The Bedford Level Experiment :

An experiment was conducted by Dr. Wallace, in the Bedford canal area in England. A set of three poles of equal heights were fixed at a distance of 5 km apart another in a straight line above the water level along of this canal.

From a telescope, it was observed that the middle pole stood taller than the other two. This further confirmed the curvature of the Earth’s surface although apparently, it looks flat.

(10) Aerial Photographs :

Numerous photographs of the Earth have been taken by astronauts showing its spherical shape.

(11) Artificial Satellites :

Pictures taken by artificial satellites show the spherical shape of the Earth. The most clinching evidence of the spherical shape of the Earth is obtained from photographs taken from space.

Is The Earth Actually Round /Perfectly Spherical?

It is now known that the shape of the Earth is not exactly a sphere. There is a slight bulging at the Equator and a flattening at the two polar regions.

This is caused by the rotation of the Earth. That is why the Equatorial diameter of the Earth (12757 km) is larger than the Polar diameter (12714 km.).

The difference of 43 km is quite small considering the larger size of the Earth. Yet the Earth is not said to be a complete sphere. This unique shape of the Earth is called ‘Oblate-Spheroid’.

Oblate Spheroid :

A sphere in Which its polar diameter is shorter than the equatorial diameter (e.g. in the case of the Earth it is so by 43 km.).

Earth’s Dimensions

(1) Equatorial Circumference    =  40,075 km.
(2) Polar Circumference            =  40,024 km.
(3) Equatorial diameter            =  12756.8 km.
(4) Polar diameter                    =  12713.8 km.
(5) Equatorial radius                =  6378.4 km.
(6) Polar radius                        =  6356.9 km.

What Is Geoid?

The Earth is not a perfect sphere. Its surface is not smooth. There are high mountains like the Himalayas (Highest peak Mt. Everest 8848 m) and the deepest part of the Earth (The Mariana Trench in the Pacific Ocean) has a depth of 11034 meters.

The difference in elevation between the highest and lowest parts of the Earth is about 20000 meters or 20 km. There are many lofty mountains, plateaus, extensive depressions, rivers, lakes, seas, etc

Those make the surface of the Earth uneven. So the shape of the Earth may not be considered to an orange or a pear. It can be most accurately described that the shape of the Earth is ‘Geoid’ which simply means ‘Earth-shaped’.

WBBSE Notes for Class 6 Junior School Geography