III. Answer the Following in Five Sentences.

Question 1.
Describe the size of the Earth ?

Answer:

• About 2,000 years ago, the Greek astronomer Eratosthenes calculated the Earth’s circumference at the equator as 41,140 km, close to the modern value.
• Actual circumference: Equatorial – 40,076 km, Polar – 40,006 km (difference – 70 km).
• Diameter: Equatorial – 12,757 km, Polar – 12,714 km (difference – 43 km), due to the geoid shape of the Earth.
• Total surface area: 510.9 million sq km → 71% water (361 million sq km) and 29% land (149 million sq km).
• Land divisions: 7 continents – Asia, Africa, North America, South America, Antarctica, Europe, Australia.
• Water bodies: 5 oceans – Pacific, Atlantic, Indian, Antarctic, Arctic, plus gulfs, bays, and seas.
• Hemispheres: Divided by the equator → Northern Hemisphere has 2/3 of the land, Southern Hemisphere has 1/3. The Prime Meridian divides Eastern and Western Hemispheres.

Question 2.
Name and explain the proofs in support of the spherical shape of the Earth ?

Answer:
There are several proofs to regard the earth as a spherical shape of the Earth.

1. Heavenly bodies appear to be spherical:
   The Sun, the Moon and other heavenly bodies appear to be spherical when viewed from different position. The earth is one of them and hence it must also be spherical in shape.
2. The Lunar Eclipse:
   The lunar eclipse proves that the Earth is in spherical shape. During lunar eclipse when the Earth is between the Sun and the Moon, the shadow of the Earth falls on the Moon. Aristotle was the first scholar to show this by looking at the shadow of the Earth on the lunar surface. Later, this was ascertained by Ptolemy. This is considered to be the oldest proof in respect of the shape of the Earth.
3. Sunrise and Sunset:
   The time of Sunrise and Sunset is not the same everywhere in the world. This is due to spherical shape of the Earth. If the Earth were to be flat all places on the Earth would have had sunrise and sunset at the same time everywhere in the world.
4. Circumnavigation:
   Circumnavigation of the world can only be possible when the Earth is in spherical shape. If one start on a sea voyage towards the east, by moving constantly in the same direction, he would be able to complete a circle of the world and reach the original point form where he had started.
5. The Bed Ford level experiment:
   Dr. Alfred Russel Wallace conducted an experiment in 1956, along the Bed Ford level canal area in Britain. It is the most convincing proof of the curvature of the Earth. He fixed three poles of same height at an interval of about mile apart and observed through a telescope. It was found that the pole in the middle was higher than other two poles. It is due to the curvature of the Earth. If the Earth were to be flat all the poles would have the same horizontal level.
6. Sighting a ship:
   A ship on the sea approaching the coast, when seen from the short does not come into view all at once. The observer first sees the mast and then the hull and finally the whole ship. A ship moving away from the coast disappears gradually and finally out of view. If the Earth were to be flat the whole ship would have come into view.
7. Aerial and Satellite Photographs:
   The photographs taken by the cosmonauts in the recent decades and satellites have provided ample proof to show that the earth is spherical in shape.

Question 3.
Explain the effects of the rotation of the Earth ?

Answer:
Rotation of the Earth causes various effects. They are:

a. Day and night caused by the rotation of the earth on its axis. This is because parts of the earth which face the sun have day and the parts which do not face the sun have night. This happen with precision and progression and not suddenly – The time when the sun beings to cast its light in the sky is known as dawn. At noon. The sun is overhead. At dusk, it is twilight and the sun is seen disappearing in the sky. At night, it is completely dark.

1. The duration of the day and night is not equal at all places on the earth because of the inclined axis. The length of days varies with respect to the seasons as well as latitude
2. The sun, the moon and the stars seem to move from east to west. This is because the earth spins from west to east. This effect is similar to what one experiences while looking at trees from a moving train.
3. The speed of rotation has created a centrifugal force resulting in a bulge in the middle portion of the earth and flattened top at the poles.
4. The earth’s rotation affects the movement of water in the oceans. The tides are deflected because of the rotation of the earth.
5. Rotation causes difference in time over various places on the earth.
6. The Earth acts as huge magnet: The one end of the needle of the compass always points towards the north magnetic pole. That means, the earth acts as a magnet. The rotation . of the earth causes the earth to act as a magnet.
7. Rotation of the Earth influences the movement of ocean water, particularly ocean currents.
8. The rise and fall in the sea level is called tides. Rotation of the Earth causes the lacing of water bodies to the Moon. The gravitational attraction of the Moon and position of the water bodies cause tides. This is a regular phenomenon due to Earth’s rotation.

Question 4.
Describe the special latitudes and temperature zones of the globe.

Answer:
Due to the Earth’s inclination of 66½° and its revolution around the Sun, certain special latitudes can be recognized on the globe. The vertical rays of the Sun strike the Earth at different points at different times of the year. On March 21st and September 23rd, the Sun’s rays fall vertically on the Equator.

On June 21st, they fall vertically on 23½° North, known as the Tropic of Cancer, and on December 22nd, they fall vertically on 23½° South, called the Tropic of Capricorn. On June 21st, the Sun’s rays reach up to 66½° South, the Antarctic Circle. The North Pole (90° N) and the South Pole (90° S) mark the ends of the Earth’s axis.