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Class 8 physics Chapter – Stars and The  Solar System  CBSE and NCERT- Suraj Sir

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Questions :  1.What are the difference between stars and planets?
Ans:
Stars are:            a. luminous                       b. Stationary
Planets are :      a. Non luminous               b. Movable

Questions :  2. What re the difference between galaxy and constellation?
Ans: (i) The first difference is that a galaxy is a collection of billions of stars whereas a constellation is a collection of only a very few stars.

(ii) The second difference is that a galaxy does not form a definite pattern which resembles the shape of an animal or a human being but a constellation appears to resemble an animal or human being in its shape

Questions :  3.  What are the asteroids?   
Answer: There is a large gap in between the orbits of the Mars and Jupiter. This gap is occupied by a large number of small bodies that revolve around the sun. These are called asteroids
Questions : 4. What is meteorites? In which bodies are meteorites craters more commonly found and why?
Ans: meteorites are rocky bodies revolving around the sun. Large meteors when hit the surface of planet create craters. Meteorites craters more commonly found on those planets and moon which have no or little atmosphere to burn off the falling rocks. E.g. Moon and mercury.

Questions : 5. What is comet? How is its tail formed?
Ans:  Comet is small body of ice and dust revolving around the sun in its elongated orbit. When comet approaches the sun, it heats up and leaves behind a stream of hot glowing gases and dust particles. We see it as a tail.

Questions :  6. Why does geostationary satellite seem fixed above a point on the earth?
Ans: A satellite placed at about 3600 km above the equator completes one revolution around the sun in 24 hrs . This makes its position fixed above a point on the earth

Questions : 7. why do other stars appear to move from east to west whereas the pole star appear to be stationary?
Ans: Pole star lies exactly above axis of the rotation of earth while other star does not. Therefore when earth rotates from west to east the star will appear to move from east to west to an observer on the earth but pole star appear stationary to same observer.
This property of pole star makes it useful to the sailors as they can locate north with the help of pole star

Questions :  8. Why Venus is hotter than mercury even if it is far away from the Sun?
Ans: Venus has highest percentage of CO2 in its atmosphere that result into greenhouse effect.

Questions : 9. why is mercury so hot during the day and cold at night?
Ans: Being close to sun, mercury turns extremely hot about 400 degree centigrade during day. As gravitational force is not enough to support hot atmosphere the temperature drops to – 200 degree centigrade.

Questions : 10. How far away is earth from the sun if sunlight takes 8.3 minutes to reach earth?
Ans: Time taken by sunlight to reach earth = 8.3 min = 498 sec
Speed of light = 3 x 10^8 m/s
Distance b/w earth and sun = 3 x 10^8 m/s x 498 sec = 1494 x 10^8 m

Questions : 11. Name the natural satellite of earth.
Answer:  Moon is the only natural satellite of earth.

Questions : 12. Define one light year.
Answer:  One light year is the distance travelled by light in one year at the speed of light.

Questions : 13. Why are the stars not visible during day time?
Answer: The stars are not visible during the day because of the glare of bright sunlight.

Questions :  14. What is a pole star?
Answer: Pole star is a star that is situated in the north direction and appears stationary to us.

Questions :  15. What is the total number of planets in our solar system? Name them
Answer: There are nine planets in our solar system. These are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

Questions :  16. Which planet is known as morning and evening star? Why is it so called?
Answer: Mercury is known as morning and evening star. It is because it becomes visible just before sunrise or immediately after the sunset and appears like a very bright star.

Questions :  17. Which day is longest and smallest in the northern and southern hemisphere?
Answer: On June 21, the earth is farther away from the sun than on December 22. On this day we have the longest day in the northern hemisphere while it is the shortest in the southern hemisphere.
On December 22, the length of the day is the shortest in the northern hemisphere and longest in the southern hemisphere.

Questions :  18. What are the asteroids?
Answer: There is a large gap in between the orbits of the Mars and Jupiter. This gap is occupied by a large number of small bodies that revolve around the sun. These are called asteroids

Questions : 19. Differentiate between meteors and meteorites.
Answer: Meteors are very small stone like objects that are revolving around the sun. When a meteor enters the atmosphere of the earth, it gets heated due to friction of air. The heat produced is so high that meteors begins to glow and evaporates within a short time.
Some meteors are so large that a part of them reaches the surface of the earth before they get evaporated completely, these are known as meteorites

Questions : 20. Write a short note on constellation.

Answer: Many a time, a group of stars as seen from the earth, appears to form some kind of pattern. Our ancestors imagined some known shapes formed by many groups of stars and gave them specific names. Such a group of stars is known as a constellation. Some easily identifiable constellations are Ursa Major or Vrihat Saptarshi, Ursa Minor or Laghu Saptarshi and Orion or Mriga.

Questions :  21. Give some practical applications of artificial satellites.
Answer: Artificial satellites have many particle applications. Long distance transmission of television programmes, communication through telephones and internet could be possible because of them. Artificial satellites are also used for research, defense and remote sensing. Some artificial satellites are also used to gather information about the movements of materials concerning defense activities.

Questions :  22. Differentiate among Ursa and Ursa minor by drawing their relative positions of stars.
Answer :  Ursa Major or Vrihat Saptarshi is known as Big Dipper. The Big Dipper is a group of many stars of which seven are comparatively brighter and are easily visible. It appears like a big ladle or a question mark. Ursa minor or Small dipper also has seven prominent stars in it. These constellations are usually visible during springs from our part of the world


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