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What is a constellation?

Class 6 ScienceNCERT chapter: Beyond Earthइसे हिंदी में पढ़ें

Exam-ready answer

A constellation is a group of stars that appears to form a recognisable pattern or shape in the night sky. People long ago imagined these patterns as animals, objects or heroes and gave them names. Examples are Orion (Mriga), Ursa Major, whose seven bright stars form the Saptarishi or Big Dipper, and Cassiopeia. Constellations help us identify stars and directions.

Explanation

On a clear, dark night away from city lights, the sky is full of stars. If we watch them for a while, some bright stars seem to link up into shapes, just as we join dots to make a drawing. Such a group of stars forming a pattern is called a constellation. Different cultures saw different pictures in the same stars and named them after their own stories.

Orion, called Mriga in India, looks like a hunter, with three bright stars in a row forming his belt; it is easy to spot on winter evenings. Saptarishi, seven bright stars shaped like a big ladle or question mark, is part of the constellation Ursa Major (the Great Bear). Cassiopeia looks like a stretched letter W or M. Today astronomers divide the whole sky into 88 constellations.

The stars of a constellation only appear close together when seen from Earth; in reality they can be at very different distances from us. Because Earth rotates, constellations rise in the east and set in the west during the night, just as the Sun does. Two stars of Saptarishi, called pointer stars, point towards the Pole Star (Dhruv tara), which stays almost fixed above the north, so travellers used it to find direction.

Points to remember

  1. Constellation: a group of stars that forms a recognisable pattern or shape in the night sky.
  2. Common examples: Orion (Mriga), Ursa Major with Saptarishi (Big Dipper), Ursa Minor, Cassiopeia.
  3. Astronomers divide the whole sky into 88 constellations.
  4. Stars of a constellation look close together but may be at very different distances from Earth.
  5. The pointer stars of Saptarishi help locate the Pole Star (Dhruv tara), which shows the north direction.

Exam tip

Define the term in one line, then draw the dot pattern of Saptarishi or Orion and label it; showing the pointer stars and the Pole Star makes the answer complete.

Questions students also ask

How is a constellation different from a star?
A star is a single huge, hot, glowing ball of gases that gives out its own light, like the Sun. A constellation is not one object; it is a group of many stars that appear to form a pattern when seen from Earth.
Why do constellations seem to move across the sky?
The stars are not racing across the sky. Earth rotates on its axis from west to east, so all stars, including the constellations, appear to rise in the east and set in the west during the night.
How can Saptarishi help us find the Pole Star?
Imagine a straight line through the two stars at the outer edge of Saptarishi's bowl, called the pointer stars, and extend it about five times the gap between them. The line reaches the Pole Star, which marks the north direction.

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