The Earth: Our Habitat - Geography NCERT Notes For UPSC

The Sun

It is made of extremely hot gases and it is the centre of our solar system. It acts as a pulling factor around which other planets and objects revolve.

The 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 these planets revolve around the Sun in an elongated orbit.
• Mercury is nearest to the Sun and it takes only 88 days to complete 1 orbit around the Sun.
• Venus is called Earth’s twin because of its same size and shape which is very much similar to that of Earth.

The Earth

• It is the third nearest and fifth largest planet in our solar system. It is slightly flattened at poles. That’s why; its shape is described as “Geoid”.
• Life favorable conditions such as presence of water, air and neither too hot nor too cold temperature etc. makes the Earth a unique planet.
• It is also called ‘Blue planet’ because its two-third part is covered with water.
• Earth has only one satellite, the Moon, which is 3, 84,400 km away from Earth.
• The Moon revolves around the Earth in 27 days; it takes exactly the same time to complete one spin.

Also Read: The Need for Space Sustainability

Asteroids

These are numerous tiny bodies which move around the Sun. They are generally found between the orbits of Mars and Jupiter. They are considered as part of the planets which exploded many years back.

Meteoroids

These are tiny rocks that move around the Sun. Sometimes, they come in contact with the Earth’s atmosphere and due to the friction, they get heated up and burn with a flash of light.  While Meteor, without being completely burnt, falls on Earth and makes hollow.

Galaxy

A galaxy is a cluster of billions of stars that look whitish. The Milky Way is such an example. Our solar system is part of the galaxy which is called the Akash Ganga. The whole universe is made of millions of such galaxies.

Interesting Points

• Jupiter, Saturn and Uranus have rings around them which are belts of small debris.
• ‘Sol’ in Roman mythology is the ‘Sun god’. ‘Solar’ means ‘related to the Sun’. The family of the Sun is, therefore, called the solar system.
• A Satellite is a celestial body that moves around the planets in the same way as the planets move around the Sun.
• A Human-made Satellite is an artificial body which is designed by scientists to gather information about the universe or for communication.
• The moon and the planets shine due to reflected sunlight (According to Aryabhata).
• Light travels at the speed of about 300,000 km per second. 
• The light of the Sun takes about eight minutes to reach the Earth.

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