Constellations

Objective

This topic gives an overview of; 

  • Constellations

Constellations

The stars forming a group that has a recognisable shape is called a constellation.

Constellations were devised by ancient people to be able to recognise stars in the sky. The shapes of constellations resemble objects familiar to those people. You can easily identify some constellations in the night sky. For this, you should know how a particular constellation looks like and where to look for it in the night sky. One of the most famous constellations which you can see during summer time in the early part of the night is Ursa Major.

It is also known as the Big Dipper, the Great Bear or the Saptarshi.

There are seven prominent stars in this constellation. It appears like a big ladle or a question mark. There are three stars in the handle of the ladle and four in its bowl.

Observe this constellation for a few hours. Do you find any change in its shape? Do you find any change in its position?  You will observe that the shape of the constellation remains the same. You will also find that the constellation appears to move in the sky from east to west.   we can locate the Pole Star with the help of Ursa Major.

This activity should be performed on a clear moonless night during summer at about 9.00 pm. Look towards the northern part of the sky and identify Ursa Major. You may get help from elders in your family. Look at the two stars at the end of Ursa Major. Imagine a straight line passing through these stars. Extend this imaginary line towards the north direction. (About five times the distance between the two stars). This line will lead to a star which is not too bright. This is the Pole Star. Observe the Pole star for some time. Note that it does not move at all as other stars drift from east to west.

During a summer night, observe Ursa Major 3-4 times at an interval of 2 to 3 hours. Also locate the Pole Star each time. Does Ursa Major appear to move from east to west? Does it appear to revolve around the Pole Star?

In fact, all the stars appear to revolve around the Pole Star. The Pole Star is not visible from the southern hemisphere. Some of the northern constellations like Ursa Major may also not be visible from some points in the southern hemisphere.

Orion is another well-known constellation that can be seen during winter in the late evenings. It is one of the most magnificent constellations in the sky. It also has seven or eight bright stars. Orion is also called the Hunter. The three middle stars represent the belt of the hunter. The four bright stars appear to be arranged in the form of a quadrilateral.

The star Sirius, which is the brightest star in the sky, is located close to Orion. To locate Sirius, imagine a straight line passing through the three middle stars of Orion. Look along this line towards the east. This line will lead you to a very bright star.

Cassiopeia is another prominent constellation in the northern sky. It is visible during winter in the early part of the night. It looks like a distorted letter W or M.

A constellation does not have only 5-10 stars. It has a large number of stars .However, we can see only the bright stars in a constellation with our naked eye. All the stars which make up a constellation are not at the same distance. They are just in the same line of sight in the sky.

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Summary

  • 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.
  • Major constellations are the Ursa Major, Ursa Minor and Cassiopeia.
  • The Ursa Major is shaped like a ladle and is also referred to as the Big Dipper.
  • A popular constellation is the Orion, which is shaped in the form of a hunter.
  • Three middle stars in the Orion lead to a brighter star in the sky, called Sirius.

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