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Constellations

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Constellations - Lesson Summary

Stars are always fascinating to mankind. They are the most beautiful celestial bodies about which mankind contemplates. Stars are luminous bodies which appear as points of light in the night sky. Our Sun is also a star. Many of the stars that we see in the sky are much bigger than the sun. But as they are quite far away from us, they appear very small. The light from the distant stars undergo atmospheric disturbances and this makes them twinkle. Many stars are several thousand light years away from the earth. A light year is the distance travelled by light in one year. 1 light year = 3 x 108 x 365 x 24 x 60 x 60 m = 9.46 x 1015 m. This is an extremely large distance. A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction is called a galaxy. There are at least 1011 galaxies in the universe. A galaxy comprises billions of stars and our sun is just one among the 100 billion stars in our own Milky Way galaxy. Possibly, each of those stars could have their own planetary system. 

A group of stars that can be identified with the shape of an identifiable object like an animal or a known object is called a constellation. There are as many as 88 constellations. Some well-known constellations are the Ursa Major, Orion and Cassiopeia. 

The Ursa Major is also referred to as the Big Dipper, the Great Bear, or the Saptarshi (in India). It consists of seven prominenet stars placed in the form of a dipper or in the shape of a bear. If we join the seven stars with imaginary lines, the shape obtained looks like a big ladle or a question mark. There are three stars in the handle of the ladle and four in its bowl. If an imaginary line joins the two stars at the edge of the ladle, it will point to the Pole star.  

The Pole star, or Polaris, is directly above earth's north pole. As the earth rotates on its axis from west to east, the stars appear to move from east to west. But the Pole star does not appear to move as it lies along the earth’s axis and is towards the north of the earth. It helps in identifying directions during the night as it stays in the same place all through the year. 

Another popular constellation is the Orion, which is shaped in the form of a hunter, and hence is also called the Hunter. The three middle stars represent the belt of the hunter. These stars lead to a brighter star in the sky, called the Sirius. 

The Cassiopeia is another constellation, which can be located in the northern sky. It is visible during winter in the early part of the night. It looks like a distorted letter M or W.  It has clusters of stars  

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