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Tuesday, 10 October 2017

Class 8th : Science - Chapter 15 : Stars and the Solar System

Stars_and_Solar_System_Science_8th_Chapter_15

Chapter 15 – Stars and the Solar System:
Q1. Fill in the blanks by choosing correct words from the following list:
(Meteorite, Pluto, moon, planets, universe, core, comet, constellation)

(i) The branch of science which deals with the study of Universe is called astronomy.
(ii) The unburnt part of the meteor which reaches the earth is called Meteorite.
(iii) The heavenly bodies which revolves around the sun are called Planets.
(iv) The heavenly bodies which revolves around the planets are called Moons.
(v) The orbit of Pluto is not in the same plane as that of the other planets.
(vi) A heavenly body with long tail, moving around the sun in an elliptical path is called Comet.
(vii) In the Core of the sun, hydrogen gas fuses with the liberation of the energy.
(viii) A group of stars which resembles an animal or some other known object is called Constellation.
Q2. Statements given below are incorrect. Write correct statements.
(i) Halley’s comet visits our solar system after 26 years.
Ans. Halley’s comet visits our solar system after 76 years
(ii) Helium gas contains most of the atmosphere of the sun and the stars.
Ans. Helium gas constitutes most hydrogen gas.
(iii) Pole Star is nearest to our solar system.
Ans. Pole Star is a part of constellation.
(iv) Astronomers have divided the sky into 68 constellations.
Ans. Astronomers have divided the sky into 88 constellations.
(v) Meteors on burning leave behind gold, dust and light.
Ans. Meteors after burning disappear.
(vi) The orbit of Neptune is different from the orbits of the other planets in the solar system.
Ans. The orbit of Pluto is different from the orbits of the other planets in the solar system.
(vii) Mars is the second planet nearest to the sun.
Ans. Venus is the second planet nearest to the sun.
(viii) Moon revolves around the earth in 21 ½ days.
Ans. Moon revolves around the earth in 27 1/3 days.
Q3. Answer the following questions:
(i) What is universe? Name six different kinds of heavenly bodies found in the universe.
Ans. The universe is the vast unimaginable space composing many heavenly bodies such as, planets, stars, sun, constellations, comets, meteors etc.
(ii) With reference to the average distance of the sun, state:
(a) The serial number of the planet earth.
Ans. The serial number of planet earth is 3.
(b) The average distance of the earth from the sun.
Ans. The average distance of the earth from the sun is 149.6.
(c) The time in which sunlight reaches the earth.
Ans. Sunlight takes 8 minutes to reach the earth.
(iii) (a) Name the natural satellite of the earth.
Ans. Moon is the natural satellite of the earth.
(b) In how many days does the satellite complete one revolution around the earth.
Ans. Moon is the satellite of the earth. It completes one revolution in 27 1/3 days.
(c) In how many days does the satellite rotate around its own axis.
Ans. Moon takes 27  days to rotate on its own axis.
(d) How does the gravity of this satellite compare with the earth.
Ans. The gravitational pull of moon is one-sixth that of the earth.
(e) State the maximum temperature on the day side and minimum temperature on the night side 
of this satellite.
Ans. On the day side of the moon, the temperature as high as 110oC and on night side of the moon the temperature could be as low as ­–150oC.
(iv) What do you understand by the following terms?
(a) New moon
Ans. After the completion of one revolution around the earth the moon comes in between the sun and the earth and is not visible at that time, hence we see darkness, this is called the new moon day. It is formed before the crescent.
(b) Full moon.
Ans. When the earth comes in between the moon and the sun, the moon appears to be full with bright light, this is called full moon day. It appears on the fifteenth day from the new moon day.
(v) (a) Define solar system.
Ans. The sun along with the eight planets and their moons constitute the solar system.
(b) Name all the planets in the solar system in the order of their distance from the sun.
Ans. Following are the names of the planets as per their distance from the sun:
1. Mercury 2. Venus 3. Earth 4. Mars 5. Jupiter 6. Saturn 7. Uranus 8. Neptune
Earlier Pluto was the ninth planet, which is now said to be vanished from the solar system.
(vi) (a) How many moons mars have?
Ans. Mars have 2 moons.
(b) Write the names of these moons.
Ans. Photos and Deimos are the two moons of the Mars.
(vii) What is comet? Why does a comet develop a tail while approaching the sun?
Ans. The bright ‘Star like’ object with a long tail approaching the sun in a highly elliptical orbit is called Comet. It is a small icy celestial body. The nucleus of comet consists of solid frozen ice, gas and dust. When the comet approaches the sun, the particles with in the nucleus get deflected due to heat radiations of the sun and it increases when it reaches close to the sun giving rise to a tail like structure.
(viii) What is star? What makes the star give about vast amount of energy?
Ans. A star is a giant ball of hydrogen gas with a bright light and heat. Due to the fusion of hydrogen gas, a heavier gas, i.e., Helium, is formed which lubricates a huge amount of heat and energy. So this is due to the fusion of hydrogen gas that the star gives about a vast amount of energy.
(ix) (a) How are meteors different from stars?
Ans. Differences between meteors and stars are as under:
(ix) (a) How are meteors different from stars?
Ans. Differences between meteors and stars are as under:

Meteors
Star
1. Consists of rocks metals and dust
2. Produces heat and light energy due to the friction of earth’s atmosphere.
3. Meteors are very small pieces of rocks.
4. Meteors last for few seconds.
1. Consists of hydrogen and helium.
2. Produces heat and light energy due to fusion and hydrogen.
3. Stars are extremely big.
4. Stars last for billions of years.

(b) How are meteors different from meteorites?
Ans. Meteors are shooting stars that produce heat and light energy due to the friction of earth’s atmosphere.
The unburnt piece of a meteor, which reaches the surface of earth is called meteorite. Its size is from size of small pebbles to several tons of rock and metal.
Additional Text Book Questions:
Page No. 190: Test Yourself
 Q1. What are celestial bodies? Name any three celestial bodies.
Ans. Celestial bodies are the heavenly bodies found in the universe. Moon, planets, sun, stars, meteors, comets etc. some celestial bodies.
Q2. Why do you classify the sun as star?
Ans. Stars emit heat and light due to the fusion of hydrogen. Sun also emits a huge amount of light and energy due to the fusion of hydrogen and the formation of helium gas. Hence sun is called a star.
Q3. Why do the stars appear like point objects?
Ans. The stars appear like point objects because they are very far away from us i.e., earth, on which we live. It is only the sun which appears bigger to us because it is nearest to earth.
Q4. What is a constellation? How does a constellation differ from a star?
Ans. A group of stars which forms a recognizable pattern or shape is called a constellation. A star is a giant ball of hot gases like hydrogen or helium, while as constellation is a group of stars.
Q5. Name a star which appears stationary from the earth. In which constellation is it situated?
Ans. Pole star appears stationary from the earth. It is situated in Ursa Minor constellation.
Q6. What is “a light minute”? How many light minutes is the earthy from the sun? Express this distance in kilometres.
Ans. The distance travelled by the light at a speed of 300,000km/s in one minute (60 seconds) is called a light minute.

1 light minute = 300,000 km/s x 1 minute

                        = 300,000 km/s x 60s

                        = 1800000 km = 18 x 106 km

Q7. How much time is involved from one new moon to another new moon as seen from the surface of the earth?
Ans. 29 ½ days of time is involved from one new moon to another new moon.
Q8. In how much time does the moon complete one rotation about its own axis?
Ans. Moon completes one rotation about its own axis in 27 .

 Page No. 197: Test Yourself

Q1. What is a planet? How many planets revolve around the sun?
Ans. A solid heavenly body which revolves around the sun in well-defined orbit is called Planet. Recent studies say that there are eight planets revolving around the sun.
Q2. Name the planet which:
(i). Is nearest to the sun?
Ans. Mercury is nearest to the sun.
(ii). Is Farthest from the sun?
Ans. Neptune is the farthest planet from the sun.
(iii). Supports life?
Ans. Earth supports life.
Q3. Name the planets which:
(i). Revolves around the sun from east to west?
Ans. Earth is the planet which revolves around the sun from east to west.
(ii). Intersects the orbit of another planet?
Ans. Pluto intersects the orbit of Neptune.
Q4. Name one planet that was predicted before its discovery?
Ans. Pluto was predicted as a planet before its discovery.
Q5. Name the planet having:
(i). Largest number of moons?
Ans. Saturn has the largest number of moons. It has 30 moons or satellites.
(ii). A system of number of rings?
Ans. Saturn has a system of number of rings.
Q6. What is the solar system? Name all the planets of solar system in the increasing order of distance from the sun?
Ans. The sun along with eight planets, three plutons, and their moons constitute Solar System.
  Following are names of planets of the solar system:
1. Mercury, 2. Venus, 3. Earth, 4. Mars, 5. Jupiter, 6. Saturn, 7. Uranus, 8. Neptune
Plutons are:
1. Pluto, 2. Charon, 3. 2003 UB313

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