Chapter 1: The Earth in the Solar system (Notes)
Posted on : 19-11-2017 Posted by : Admin

Introduction

1. A galaxy is a huge system of billions of stars and clouds of dust and gases. Millions of such galaxies make the universe. Our solar system is a part of Milky Way Galaxy.
2. The Milky Way is a part of pace with tons and tons of stars crowded together — This crowd of stars resembles path with spilled milk.  And so the name "Milky way".
3. Ancient Indians named the Milky way galaxy as named Akash Ganga based on the imagination that it is a river of light flowing in the sky.
4. The sun, the moon and all the objects shining in the sky are called as the Celestial bodies.
5. The celestial bodies having the heat and light of their own are called as the Stars.
6. The various patters formed by different groups of stars are called as Constellations. Eg: Ursa major/Big bear; Sapta rishi (Seven sages) /Small bear
7. Sapta rishi can be easily recognized in the sky. Ancient people used to determine directions with the help of this constellation.
8. The North Star indicates the north direction and it always remains in the same position in the sky. It is called as the Pole star. The position of the pole star can be determined by drawing and extending an imaginary line joining the pointer stars.
9. A new planet UB313 has been recently discovered which is bigger than Pluto and farthest from the sun.
10. UB313 is the largest Dwarf planet. It is the ninth largest body known to orbit around the sun. It is discovered by Mike brown in Jan 2005. It is called as Eris. And its Informal name is Xena.
11. Light travels at a speed of 300, 000 km/sec. With this speed the light of sun takes about 8 minutes to reach earth.

 

The Solar System

• The word solar system is derived is derived from Roman mythology. 'Sol' is Sun god and 'Solar' related to Sun.
• The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system.
• The sun is the head of the solar system.

 

The Sun

• The sun is the centre of solar system.
• It is huge and made up of extremely hot gases. The pulling force of the sun binds the entire solar system.
• The sun is the ultimate source of heat and light for the solar system.

 

Planets

• The celestial bodies that do not have the light or the heat of their own are called as Planets.
• The word ‘planet’ comes from the Greek word ‘Planetai’ which means wonderers.
• There are eight planets in our solar system-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 elongated. They are called orbits.
• Jupiter, Saturn and Uranus have rings around them. These are belts of small debris. These rings may be seen from the earth with the help of powerful telescopes.
• Mercury is the nearest planet and Neptune is the farthest planet from the sun.
• Venus because of its shape and size is similar to the earth is considered as 'Earth's-twin'.
• Till August 2006, Pluto was also a planet. But now it is called dwarf planet.

 

The Earth

• The earth is the fifth largest planet in size and the third nearest planet to the sun and is our home.
• It is slightly flattened at the poles. That is why its shape is called Geoid.
• Earth gets its light and heat from Sun which is our nearest star. 
• From the outer space, the earth appears blue because its 2/3rds surface is covered by water. It is, therefore, called a blue planet. 
• When earth is seen from the moon it appears shining just like the moon.

 

Satellites

• It is a celestial body that moves around the planets in the same way as the planets move around the sun.
• Human-made Satellite is an artificial body. It is designed by scientists to gather information about the universe or for communication.
• Artificial satellite is carried by a rocket and placed in the orbit around the earth.
• Some of the Indian satellites in space are INSAT, IRS, EDUSAT, etc.

 

The Moon

• Our earth has only one natural satellite that is the moon.
• Moon appears so big because it is nearer to our planet than other celestial bodies.
• The moon moves around the earth in about 27 days and 8 hours. It takes exactly the same time to complete one spin of earth. This makes only one side of the moon visible from the earth.
• The moon does not have conditions favorable for life. The surface of the moon is covered with plains, mountains and depressions which is observable as shadows on full moon day.
• Neil Armstrong was the first man to step on the surface of the moon on 29 July 1969.

 

Asteroids

• There are numerous tiny bodies which also move around the sun. These bodies are called asteroids.
• They are found between the orbits of Mars and Jupiter.
• The scientists believe that these are the parts of a planet, which are formed by the explosion of that planet many years ago.

 

Meteoroids

• The small pieces of rocks which move around the sun are called meteoroids.
• Sometimes these objects come close to the earth and drop upon it. While dropping on the earth they get heated up and burn due to friction with the air and appear as a flash of light.
• Meteors sometimes do not get burnt completely and strike the earth surface creating a hollow.

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