Constellations
Category : 8th Class
Constellations
Thousands of stars appear in the sky during the night. Some of these stars form a pattern in a group, which have recognizable shape. This group of stars is called constellation. At present there are about 88 constellations. Each constellation has been given a name according to its shape. Some of the important constellations are Ursa Major, Ursa Minor, Orion, Leo Major and Cassiopeia.
Ursa Major: It is also known as Great Bear or Saptarishi. It consists of seven bright stars, which appear in the shape of a bear. It is visible during the summer season in the early part of the night and can be seen clearly during the month of April in the northern part of the sky. It also helps us to locate the position of the pole star in the sky. At night it appears to move from east to west as the pole star remains fixed in its position.
Orion: This constellation is also known as hunter. The Indian name is Mriga. It consists of seven or eight bright stars. The orientation of stars in Orion is similar to the figure of hunter. This constellation is visible in the sky during the winter season in the late evening. One of the brightest stars in the sky at night is the Sinus, which is very close to the Orion constellation.
Leo Major: This constellation mainly consists of 9 or 10 stars. Its orientation is similar to that of lion, hence its name is Leo. It is visible during the summer in the early part of night.
Cassiopeia: It mainly consists of five stars, which are arranged in the form of letter W or M depending on its position in the sky. It is supposed to represent an ancient queen named Cassiopeia. It is visible during the winter in the early part of the night.
Constellation is formed by the group of stars forming different pattern. These groups are named according to the shape of pattern they resemble. Which one of the following is also the name of the constellation Ursa Major?
(a) Mriga
(b) Leo
(c) Night Queen
(d) Saptarishi
(e) None of these
Answer: (d)
Each constellation is made up of different number of stars arranged in different pattern. Orion is one of the constellations. The number of stars of which Orion is made up of is_________.
(a) 5 or 6
(b) 7 or 8
(c) 9 or 10
(d) 100
(e) None of these
Answer: (b)
Explanation
The number of stars in Orion is 7 to 8.
Life of Star
The stars are formed from the existing gas and dust in the outer space. This gas and dust is called interstellar matter. When these lumps of gases and dust cross the spiral arm of the galaxy, they start to form clumps. The gravitational force within cause them to contract, forming protostar. When the temperature at the centre of the protostar reaches several million degree Celsius, fusion reaction begins. The energy released by this reaction prevents the protostarto contract, and hence a star is born.
These stars are mainly made up of hydrogen gas. A hydrogen atom consists of electron and proton. Its nucleus does not contain neutron. The gravitational force within the star compress the matter at the centre causing the proton within the nucleus to collide. The hydrogen nuclei combines together to form bigger nuclei called helium nuclei, releasing large amount of energy. This energy helps stars to twinkle at the night. The light released by the stars is of different colours. The difference in the colours of the stars is due to the difference of their temperature.
The core of the star is made up of hot and compressed helium. When the temperature at the core reaches up to 200 million degree Celsius, the helium in the nucleus began to react with itself and forms heavier elements, such as, carbon. Nitrogen or Oxygen. They produce energy that stop the star from contracting. The outer layer becomes so large, the star starts loosing it. This stage of the star is called planetary nebula. At this stage, it becomes blue white star, where the temperature of the core rises, causing the layer surrounding the core to expand. Such stars are called White Dwarf. It is made up of ice, carbon and oxygen. After this, it starts to cool over a period of thousand million years and becomes black hole. In this way, the life of a star ends.
There are various stages of the life of the stars. During these phases, the stars undergo various changes in its feature. The second stage of the life of the star is called:
(a) Shooting star
(b) White dwarf
(c) Protostar
(d) Black hole
(e) None of these
Answer: (c)
When we study the life of the star from its birth to death, we find that at some stage it expands due to high inner temperature and at other stage in starts contracting due to loss of heat from its core. The stage of stars life, when it starts loosing its outer layer due to its large size as a result of expansion, is called____.
(a) Fusion
(b) Breaking crest
(c) Planetary Neubia
(d) Planetary star
(e) None of these
Answer: (c)
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