Earth, our home is the third planet in the solar system and the only planet known to have an atmosphere that has free oxygen, oceans of water on its surface land, and, of course, life. Do you know the true shape and size of the earth?
Shape and Size of Earth: The Shape
In ancient times it was believed that the shape of the earth is flat like a disc and it had steep edges. They thought that they would fall off the edges.
But why do you think it never happened? It never happened because the Earth is not flat, it is spherical in shape. But it is not a perfect sphere either, as it is bulging at the Equator and flattened at the Poles. Therefore, the shape of the earth is said to be Oblate Spheroid. The shape of the earth is also described as Geoid, which means earth shaped.
Do you know about the first person who stated that the earth is not flat, but spherical in shape?
In the 6th century, the famous Greek Philosopher, Pythagoras said that the earth was spherical in shape. Later on Aristotle, Varahmihira, Aryabhatas, and Copernicus also said that Earth is spherical in shape.
Shape and Size of Earth: The Size
The earth is one of the smaller planets in the solar system. Jupiter is the largest planet in the solar system whose diameter is 11 times that of the earth. Earth is the fifth-largest planet in our solar system.
Earth in the Solar System
But how do we know about the size of the Earth? The first attempt to measure the size of Earth was made by Eratosthenes in the third century B.C.
He calculated the size of the earth by comparing the angle of the sun’s ray at Syene in Aswan and at Alexandria in Egypt. This distance, however close to the real figure was not accurate and modern scientists have made these calculations very precisely with advanced instruments.
Now, according to NASA’s (National Aeronautics and Space Administration) Goddard Space Flight Center, the radius of Earth at the equator is 3,963 miles (6,378 km). However, Earth is not quite a sphere, therefore, earth’s polar radius is 3,950 miles (6,356 km).
Questions on Shape and Size of Earth
1. How was the shape of the earth thought to be, in ancient times?
2. What is the actual shape of the earth?
d. Oblate Spheroid
3. Who was the first person to state that the shape of the earth is spherical?
Earth is the ________largest planet in our solar system.
4. What is the radius of Earth at the equator?
a. 6,400 km
b. 6,318 km
c. 5,378 km
d. 6,378 km
Important Proofs to support the spherical shape of the Earth
1. The sun and the other planets: First proof states that in the solar system, all the heavenly bodies are spherical in shape. Therefore, the earth cannot be an exception. Hence, the shape of the earth should be spherical.
2. The sunrise and the sunset: This came out as very strong proof. As we observe the sun rises in the east and sets in the west. The time of the sunrise and the sunset is not the same everywhere. We know that the earth rotates around its axis from west to east, so people living in the eastern areas see the sunrise earlier than the people living in western areas. If we consider that the earth is flat, then we all will see the sunrise and the sunset at the same time. Do you know which country receives the first sunlight? Japan receives the first sunlight each day.
3. The circular Horizon: We all must have observed at least once in our life that if we look around from any place, whether a hilltop or from a tall building, the edges of the Earth or horizon look circular in shape. The extent of this circular horizon increases with the increase in altitude of the observer. Do you think we would observe the same if the earth were flat?
No, because it is only possible when the shape is round and in this case, spherical.
4. The Circular Shadow: Aristotle observed the circular shadow (an arc of shadow) of the earth on the moon during a lunar eclipse. It was not possible for a flat body to cast a circular shadow. This gave the conclusion that the shape of the earth is spherical.
5. The Sighting of a ship: While standing on the sea coast, if we watch a ship approaching the land, first we will see the smoke coming out of the chimney of the ship (because the entire ship lies below the line of sight). As the ship comes up over the horizon, we can see the chimney, then the deck, and finally the entire ship. This is because of the curved surface of the Earth.
6. The pole star: Do you find the pole star overhead (at 90 degrees) at all the places on the earth?
No, because it can only happen if the earth is flat which is not true. The position of the pole star is always vertically above the North Pole. The angle of the elevation of the pole star is different at different places. This angle decreases towards the equator, where it is 0 degrees.
7. The Circumnavigation: In history, there is a great record of this proof. In the early years of the sixteenth century, Ferdinand Magellan, a Portuguese navigator, and explorer went on a voyage and discovered the Strait of Magellan. He sailed across the pacific ocean and was killed in the Philippines. But his ship, Victoria continued westwards and finally completed the voyage around the world and proved that the earth is spherical in shape. This is why, the sailors who travel around the world in different directions, usually come back to the starting point.
8. The Bedford Canal Experiment: The most convincing proof about the shape of the earth was given by a Britisher, Dr. Wallace, who carried out an experiment in the Bedford canal area in England. He fixed three poles of equal length on the level bed of the Bedford canal at a distance of one mile or 1.6 km from each other. It was ensured that the three poles had the same height above the water in the canal.
Dr. Wallace observed the top parts of these poles with the help of a telescope. He found that the middle pole was higher by about eight inches or 20 cm. This experiment was repeated in several other directions and at different places. It proved beyond doubt that the surface of the earth is curved and the earth is spherical in shape.
9. Recent photographs of the earth: Although it has been proven that the Earth is spherical in shape, nowadays the orbiting satellites have taken photographs from different angles and heights. In those pictures, we can clearly see that the Earth is spherical in shape.
MCQ Questions on the shape and size of earth
1. The earth rotates around its axis from __________.
a. North to south
b. South to North
c. East to West
d. West to East
2. How does the horizon appear from the top of a high building?
c. Square Shaped
3. Who observed a circular shadow of the earth during the lunar eclipse?
4. Who was Ferdinand Magellan?
a. A Chinese explorer
b. A Greek Philosopher
c. An Indian Explorer
d. A Portuguese Explorer
5. The Bedfort Canal Experiment was conducted by _______________.
a. Dr. John
d. Dr. Wallace
Exercises on the shape and size of earth
Fill in the blanks:
- The shape of the Earth is also described as Geoid, which means earth shaped.
- The earth’s polar radius is 3,950 miles.
- Ferdinand Magellan discovered the Strait of Magellan.
- The first attempt to measure the size of the earth was made by Eratosthenes.
- Japan is the first country to reveive sunlight daily.
True or False
- Pythagoras stated in the 6th century that the earth was spherical in shape. True
- The diameter of the Jupiter is double of that of the earth. False
- NASA stands for Northern Aeronautics and Space Association. False
- The angle of elevation of the pole star decreases towards equator. True
- The three poles used in the Bedfort Canal experiment were of different heights. False