The Earth, as we know, is a member of the planetary system of the Sun. Besides the Sun, the solar system includes nine planets, their satellites, asteroids and comets.
The planets are located in the following order away from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The Earth is situated approximately 150 million kilometers away from the sun.
Before Copernicus demonstrated that the Sun is the centre of our solar system, the ‘Geocentric Theory’ regarding the Earth was getting wide acceptance. According to this theory, the Earth was the unmoving centre of the universe, round which the Sun and the stars and all other heavenly bodies revolved.
The ‘Heliocentric Theory’ evolved by Copernicus stated that the Sun was the centre of the universe and that the Earth and other planets revolved round it. The belief that Sun was the centre of the universe was corrected by the German astronomer Johan Kepler in 1609.
Galileo Galilei, the Italian astronomer and Sir Isaac Newton, the German scientist, had conclusively established that the Sun is the centre of the solar system. Modern theories on the Earth are based on the Copernican theory.
All the planets of the solar system are divided into two groups. The inner planets i.e. those of the terrestrial group, which are nearer to the Sun and are the denser members of the solar system and include Mercury, Venus, the Earth and Mars.
The outer planets are bigger in volume and lighter in density. They include Jupiter, Saturn, Uranus, Neptune and Pluto.
The Earth, the planet on which we live has the highest density among terrestrial group of planets. It has one satellite, the Moon. The Earth is unique amongst the planets of the solar-system in possessing a complex variety of living forms and an atmosphere of a nitrogen composition.
The following are some of the important facts about the Earth:
1. The shape of the Earth is that of a spheroid.
2. Its equatorial radius is 6378.3 km.
3. Its polar radius is 6356.9 km.
4. Mean radius is 6371.2 km.
5. Mass of the Earth = 5.975 x 1027 gm.
6. Volume of the Earth = 1.08 x 1027 cc.
7. Avenge density – 5.5 gm/cc.
8. Average density of surface rocks is nearly 2.8 gm/cc.
9. Age of the Earth = 4.5 billion years.
10. Area of the Earth’s surface = 510.08 million square km.
11. Total Land-surface = 148.63 million square km.
12. Total water-surface = 361.45 million square km.
13. The Earth completes one full rotation around its axis in 23 hours 56 minutes.
14. The Earth completes a full revolution around the Sun in 365.26 days.