The most important planet to us is the Earth that distinguishes itself from other heavenly bodies of the solar system in respect of the following facts.
(a) It is the largest of the minor or inner group of planets.
(b) The earth, with a radius of about 6400 km and large circumstance of about 40,000 km, might seem to be large enough but in fact, this whirling planet is but a tiny speck in the astoundingly vast Universe.
(c) It is the only planet of the solar system and the only member of the myriads of systems in the universe, which presents an intermingling condition of air, water and land. Thus, it is unique among the planets having abundant water, an atmosphere and surface temperature condif that have supported life.
It is the only planet known till date where living being including intelli creatures like man exists. The other planet where probability of life surmised is the Mars.
Unlike other planets, the Earth has a strong magnetic field of its own, It is the densest planet. It shows evidences of erosion of its suit (change of landforms by actions of air and water etc.) which is complet lacking in other planets.
While in other planets and satellites there are innumerable meteoritic era (depressions made by impact of meteorites), the Earth's surface shows m less evidence of such craters which are very much modified by erosion.
Physical Aspects of Earth: The following physical aspects of the Ea are noteworthy.
Slight flattened sphere (oblate spheroidal) the figure of the ea corresponds to an imperfect sphere.
The idea of earth's shape as an oblate sphere with slight flattening at i poles and bulging at the equator was propounded by Newton in 17th century. According to Newton, the earth being a rotating sphere would subject to centrifugal flattening in the Polar Regions. Thus, the ea departed from perfect sphere and would be roughly orange-shaped. This i attested by the fact that the equatorial diameter of the earth is about 42 lr greater than the polar diameter.
The idea of Pear-shaped earth was first proclaimed by Sir James"Jeans by the beginning of 20th century. The latest measurements by artificial satellites confirm the idea of Jeans and indicate the shape to be a slightly flattened sphere with some irregularities at the north and south poles. Thus, the shape of the earth as per the latest computations is more nearly PEAR- shaped than orange-shaped.
Earth is an average-sized planet in the solar system. Latest data based on geodesic survey (Geodesy deals with the study of measurement of dimensions of the Earth) and satellite observation, speak of the following measurements relating to the dimension (size) of the Earth.
12,755 km 12,713 km 12,742 km 40,075 km 40,008 km
510 million square kms 1.08 x 1027 cc 5.976 x 1027gm
The difference between equatorial and polar diameters of the earth (12,755 - 12713 = 42 km.) indicates the bulging and flattering of the earth at the equator and poles respectively.