Chapter 1 The Earth in the Solar System Class 6 Notes geography

The Solar System

The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system.

The Sun

The sun is in the centre of the solar system. It is huge and made up of extremely hot gases. It provides the pulling force that binds the solar system. The sun is the ultimate source of heat and light for the solar system. The sun is about 150 million km away from earth.

Planets

There are eight planets in our solar system. In order of their distance from the sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All the eight planets of the solar system move around the sun in fixed paths. These paths are called orbits. Mercury is nearest to the sun. It takes only about 88 days to complete one round along its orbit. Venus is considered as ‘Earth’s-twin’ because its size and shape are very much similar to that of the earth. Till recently (August 2006), Pluto was also considered a planet. However, in a meeting of the International Astronomical Union, a decision was taken that Pluto, like other celestial objects (Ceres, 2003 UB313) discovered in recent past may be called ‘dwarf planets.”

The Earth

The earth is the third nearest planet to the sun. In size, it is the fifth-largest planet. It is slightly flattened at the poles. The Earth shape is described as a Geoid. Conditions favourable to support life are probably found only on the earth. It has water and air, which are very essential for survival. The air has life-supporting gases like oxygen. From the outer space, the earth appears blue because its two-thirds surface is covered by water. It is also called a blue planet.

The Moon

Moon is the earth’s satellite. Its diameter is only one-quarter that of the earth. It appear so big because it is nearer to our planet than other celestial bodies. It is about 3,84,400 km away from us. The moon moves around the earth in about 27 days. It takes exactly the same time to complete one spin. As a result, only one side of the moon is visible to us on the earth. The moon does not have conditions favourable for life. It has mountains, plains and depressions on its surface. These cast shadows on the moon’s surface.

Asteroids

Asteroids are tiny bodies that move around the sun. They are found between the orbits of Mars and Jupiter. Scientists are of the view that asteroids are parts of a planet, which exploded many years back.

Meteoroids

The small pieces of rocks, which move around the sun are called meteoroids. Sometimes, these meteoroids come near the earth and tend to drop upon it. During this process due to friction with the air, they get heated up and burn. It causes a flash of light. Sometimes, a meteor without being completely burnt falls on the earth and creates a hollow.

A cluster of millions of stars is called the Milky Way galaxy. Our solar system is a part of this galaxy. In ancient India, it was imagined to be a river of light flowing in the sky. Thus, it was named Akash Ganga.

Galaxy – A galaxy is a huge system of billions of stars