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Unit-i : geography
Chapter 1 the earth in the
solar system
Sky is an endless ceiling, where we see many shiny objects. All these objects are called
celestial bodies or heavenly bodies. The heavenly bodies include the stars, planets,
satellites, asteroids, comets, meteors, etc. The sun is also a star and our Earth is a planet.
StarS
The celestial bodies which have their own light, are called stars. Stars are made of hot and glowing
gases and produce heat and light. Stars look very small because they are so far away from us.
The sun looks bigger than other stars because it is closer to the earth.
Our sun and all the stars belong to a galaxy. There are millions of galaxies in the universe.
Our solar system belongs to the Milky Way Galaxy, popularly known as the Milky Way (Akash
Ganga). The Milky Way has about 10,000 crore stars. Short astronomical distances, such as the
distance from the earth to the sun, can be measured in kilometres. The distance is equal to
148,800,000 kilometres. But even the kilometre is too small to measure the distance between
stars. So astronomers use a unit of distance called the light year for this purpose. A light year
is the distance light travels in one year. Light travels at about 300,000 kilometres per second.
So in one year, light travels a distance of about 9.5 trillion kilometres.
Calculating distance of 1 light year
distance = ( 300,000 × 60 × 60 × 24 × 365)
Speed 1 min 1 hr 1 day 1 year
per second
= 9.4608 × 1012 km Earlier, Pluto was ninth planet
= 9.5 trillion km (rounded up) of our solar system, but now it is
considered as a dwarf planet.
the Solar SyStem
The solar system consists of the sun, the eight planets, their satellites and thousands of
other smaller bodies. The four planets that are nearest to the sun, are called inner planets.
In order from the sun, they are Mercury, Venus, Earth and Mars. Jupiter, Saturn, Uranus
and Neptune are outer planets. Mercury is closest to the sun and has almost no atmosphere
because it has been burned off
by the Sun. Venus is considered
as Earth’s twin because its
size and shape are very much
similar to that of the Earth.
Star, The Milky Way The Sun
Social Studies-6 5
