# The Earth : Shape and Size

## Shape of the Earth

Pythagoras(572-500 B.C.), a Greek philosopher and mathematician, was among the first to suggest that the Earth was shaped like a globe.

## Shape of the Earth

» If the Earth were a flat disc, then the rising Sun would have been seen at all places at the same time. But this does not happen. Places in the east see the rising Sun earlier.
» When a ship approaches land, its funnel or mast is seen first and then the hull. If the Earth had been flat, the whole ship would have been seen at the same time.

## The Earth is a sphere

» The Earth is rarely oriented in the same position during successive eclipses but it always casts a circular shadow, thus proving that the Earth is a sphere. A sphere is the only solid body that will always cast a circular shadow.
» At the North Pole, the Pole Star can always be observed at 90 degrees in the sky, since the star lies in the line with the axis of the Earth.
» As one travels southwards, the angle of Pole Star decreases.
» At the Equator the angle becomes zero degree.
» This observation proves that the path of travel is an arc of a circle.
» The Sun, Moon and all the heavenly bodies appear to be spherical when viewed from different positions. It seems logical to conclude that the Earth is no exception.
» The photographs of the Earth taken from the space prove beyond any doubt that the Earth is a sphere.

## The Earth as an Oblate Spheroid

Refined measurements of the Earth have proved that the true form of the Earth resembles a sphere that has been compressed at the poles and made to bulge at the Equator. This form is known as an oblate spheroid.

## The various factors which make the earth suitable for life to evolve and survive are

» The earth has all the essential elements like carbon, hydrogen, nitrogen and oxygen, which act as building block for the origin of life.
» The earth is neither too hot nor too cold. It has the right temperature range for carrying out the life sustaining chemical reactions.
» The earth has a lot of water in the form of lakes, rivers and oceans for the growth and survival of life.
» The earth has enough oxygen gas in its atmosphere for the survival of living beings through breathing.
» The earth has a protective blanket of ozone layer high up in its atmosphere to save life from harmful ultraviolet radiations coming from the sun.
» Biodiversity changes increase towards equator. Biodiversity is the degree of variation of life. It is a measure of variety of organisms present in different ecosystems. It is richest in the tropics.

## Statistical Data of The Earth

The Earth, third planet from the Sun, is the fifth largest planet in the Solar System in terms of size and mass.

 Age 4,550 million years Mass 5.9726 x 1024 kg Volume 108.321 x 1010 km3 Mean Density 5514 kg / m3 Total Surface area 51,00,66,000 sq.km Total Land area 51,00,66,000 sq.km Total Land area 14,84,29,000 sq.km (29.1%) Total Ocean area 36,16,37,000 sq.km (70.9%) Total Water area 38,26,72,000 sq. km Equatorial diameter 12,756 km Equatorial radius 6,378.1 km Polar diameter 12,713.6 km Polar radius 6,356.8 km (IUGG) Equatorial circumference 40,077 km Polar circumference 40,009 km Highest land point (Mt. Everest, Nepal) 8,850 m Lowest land point (Dead Sea, between Jordan and Israel) 400 m/1,300 ft (approx.) Greatest ocean depth (Mariana Trench in Pacific Ocean, near Japan) 11,033 m. (36,201 ft) Maximum distance from the Sun (At Aphelion) 152 million km (approx.) Minimum distance from the Sun (At Perihelion) 147 million km (approx.) The mean distance from the Sun 14,95,98,262 km (1.0 AU)