Ch-1: The Earth and Solar system

Celestial bodies: 

The sun, moon, stars and all other objects shining in the sky are celestial bodies. 

Stars: 

Stars are very big celestial bodies made of gases. They have their own heat and light and emit in large amounts. Our sun is also a star, near to earth. So that we can feel heat and light of sun but not other stars as they are very far away from earth. 

Constellations:

Constellations are different groups of stars form various patterns in the sky. Ursa Major (Big Bear) is one of such constellations. Saptarshi is the part of Ursa Major

Pole Star:

Pole star is also known as 'North star'. People used to determine directions during night with help of stars, particularly Pole star indicating north direction. It always remains in same position in the sky. We can locate position of pole star with the help of Saptarshi constellation. 

Planets:

Greek work 'Planetai' represents "Wanders". Planets are celestial bodies shine by light of other stars. They do not have heat and light. They move around stars. Our earth is also a planet getting light and heat from sun. 

Satellite: 

Satellites are celestial bodies, which move around planets. We have moon as such satellite. Like we have moon, other planets may also have satellites as moons. 

Sun:

Sun is the star, located at center of Solar system. It is made up of extremely hot gases. Sun provides pulling force that keeps solar system in position. Sun is about 150 billion km away from earth.

Planets in Solar system:

As pluto is considered as dwarf planet, there are 8 planets in our solar system. In order of distance, they are 

Mercury, Venus, Earth, Mars, Jupitor, Saturn, Uranus and Neptune

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These planets move around sun in fixed paths known as orbits. 

Earth: 

Earth is 3rd nearest planet and 5th large planet. It is slightly flattened at poles, so shape is described as Geoid (Earth like shape). The conditions are favorable to support life. It is neither too hot nor too cold. Earth appears blue in color when seen from outer space due to the reason its 2/3rd of surface is covered with water. So is called as "Blue Planet"

Human made Satellite:

 These are artificial bodies designed by scientists to gather information about universe or for communication. It is carried by rocket and placed in orbit around earth. Some Indian satellites are INSAT, IRS, EDUSAT etc.

Moon:

Earth has only satellite, Moon. Its diameter is 1/4th of that of earth. It appears bigger than other planets as it is near to earth. It is 3.84,000km away from earth. Moon revolves around earth in 27 days and interestingly it takes the same time to complete one rotation about its axis. This is the reason that we see only one side of moon every time. 

Asteroids:

Asteroids are tiny bodies that move around sun. They are found between Mars and Jupiter as asteroid belt. Scientists have a view that the asteroids are parts of planets which exploded many years back

Meteoroids:

Meteoroids are tiny pieces of rocks which move around sun. Some times they come near to earth and tend to drop on it. They get heated due to friction with air in this process and cause flash of light. Sometimes meteoroids which do not burn completely strike the ground and create hollow space. 

Galaxy: 

Galaxy is the huge system of billions of stars and clouds of dust and gases. There are millions of such galaxies that make universe. It is difficult to imagine how big the universe it. Our solar system is the part of Milkyway galaxy. In ancient India, it is imagined to be a river of light flowing in sky, thus names as 'Akash Ganga'.