Solar System Inferior Planets,Superior Planets,Terrestrial Planets

SOLAR SYSTEM:

The Solar System consists of the Sun, the 9 Planets that revolve around it (including the Earth), their 60 satellites (moons) and thousands of rock-like debris collectively called asteroids.The 9 planets in order of increasing distance from the Sun are: Mercury, Venus, Earth Mars, Jupiter, Siam, Uranus, Neptune and Pluto. For having some features common with the Earth and consisting entirely of rocky materials and metals, Mercury, Venus, Earth and Mars are called the terrestrial planets. The giant planets - Jupiter, Saturn, Uranus and Neptune are beyond them. Pluto, of the size of Earth, lies beyond the orbit of Neptune.

CLASSIFICATION OF PLANETS:

Inferior Planets:

The two planets --- Mercury and Venus ---that move within the Earth' orbit are known as inferior planets These planets move at a pace faster than the earth and pass between the Sun and the Earth in their orbits round the Sun. This position i.e., their coming in between the Earth and the Sun is called inferior conjunction. Occasions when one of them appears to cross the face of the Sun are called transfix. As the Mercury and Venus orbit the Sun at different angles they, therefore, do not always pass directly between the earth and the Sun. On an average there are 13 transits of Mercury in each century, Transits of Venus are much rarer. The last occurred in 1882 and the next will not be until the year 2004.

Superior Planets: 

The planets which have orbits outside that of the earth are known as superior planets. Their behavior is somewhat different; they travel slowly round the Sun. They are therefore overtaken by the earth in its revolution round the Sun. On occasions the Earth, Sun

and these planets lie in the straight line with the earth in the middle. Such a position is called"opposition",

Terrestrial Planets:

The four inner most planets viz Mercury, Venus, Earth and Mars are collectively known as terrestrial planets because of their features common with the earth. These planets are all small bodies of relatively high density composed mostly of rock minerals and

metals. Mercury with 40 per cent of Earth's diameter has an axial rotation period (rotation on its own axis) of 58.7 days. Venus has nearly the same size as that of the Earth but it is a hot and

hostile world permanently shrouded in a cloud. It completes its rotation in 243 days. Earth has a surface that is 30 per cent land and 70 per cent water. It is the only planet where the life is know to 

exist. Mars with half the diameter of the Earth is a chilly world.

Jovian Planets: 

The four giant planets viz Jupiter, Saturn, Uranus, and Neptune are often called as Jovian planets because in some respects they all resemble Jupiter. Composed mainly of hydrogen and helium they are less dense than the terrestrial planets.