SUN AND SOLAR SYSTEM
JKBOSE Solutions for Class 8 Science
JKBOSE Solutions for Class 8 Science :
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JKBOSE Solutions for Class 8 Science
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JKBOSE Solutions for Class 8 Science
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CHAPTER 15 SUN AND SOLAR SYSTEM
INTRODUCTION
Where ever we see above to the sky a vast majority seems empty and in this space are dwindling natural bodies this unimaginable space is called universe. Or The vast unimaginable space whiche encompasses most distant stars, planets and anything else, which exists is called universe and the science which deals with it is called astronomy so we can say astronomy is the the study of universe.
When we see in the night sky we see little bright light points commonly called stars but what we see are not all stars but there are planets ,satellites meteors etc too. During the day-time, we see a bright ball of fire in the sky which appears to move from the east to the west. We call it the sun.
At night, we see thousands of stars in the sky. If we watch the sky through a telescope we may see millions of stars, some of which are brightly coloured. We see certain groups of stars which appear to be in clusters. They are called constellations.
There is the moon whose size changes every day. The moon is a satellite of the earth which completes one revolution around the earth in 27.5 days. Furthermore,we see an occasional comet. It appears as a ball of fire, having a tail. Then, there are shooting starts or meteors. They appear to fall from the sky. In addition to it, there are planets like the morning stars.Bodies such as the earth, moon,planets, sun, stars, meteors, comets, etc are called heavenly or Celestial bodies.The description of all these are given below...
Universe :
The sum of everything that exists in the cosmos i.e everything under consideration is called universe it is an entity or one component of a larger entity known as the multiverse. Some times space and time or all its contents is called universe.
Natural or Celestial body:
It is defined as A natural occuring object which is located outside of Earth's atmosphere or space such as a comet, an asteroid, the Moon, a planet, the Sun, or a star.
Star:
It is a luminous celestial body which is made up of plasma mainly hydrogen spherical in shape looking like a dot whose position is fixed relative to other dots e.g sun. The largest known star is UY Scuti believed to be 1700 times larger than the sun ,the brightest star is Sirius A and B. The brightest star in the univers is Sirius, also known as the “Dog Star” or, more officially, Alpha Canis Majoris, for its position in the constellation Canis Major. Sirius is a binary star dominated by a luminous main sequence star, Sirius A, with an apparent magnitude of -1.46. The smallest known star is EBLM J0555-57Ab, the star is located some 600 light-years away in our Milky Way galaxy. Nearest star to our earth is the star Proxima Centauri. It is a companion star to the binary star system Alpha Centauri AB and is approx 4.2 light-years away from Earth.
Planet:
It is a non luminous celestial body which revolve around the star like seven planets of sun earth mercury etc. Each of the seven major bodies which move relative to the fixed stars in the night sky Mercury, Venus, the Sun, Mars, Jupiter and Saturn.
Stallite:
it is also a celestial body which revolves around the plant e.g Moon.The surface of the moon is rugged. Itis made of very large craters (deep depressions or holes) and very high mountains. It has no atmosphere, and hence, no life on it and Its gravitational pull is one sixth that the earth, same side of moon is facing towards the earth. On the day side of the moon, the temperature could be as high as 110°C. On the contrary, the temperature on the night side of the moon could be as low as - 150°C.
Meteor:
It is a fast-moving streak of light in the night sky believed to be caused by the entry of extraterrestrial matter into the earth's atmosphere; a shooting star or falling star. It is an atmospheric or meteorological phenomenon. These were sometimes classified as aerial or airy meteors (winds), aqueous or watery meteors (hydrometeors: clouds, rain, snow, hail, dew, frost), luminous meteors (rainbows and aurora), and igneous or fiery meteors (lightning and shooting stars).
Meteorite:
it is a metallic or stony object or body that is the remains of a meteoroid usually fallen on the earth's surface.
Comet:
A small Solar System body consisting mainly of volatile ice, dust and particles of rock whose very eccentric solar orbit periodically brings it close enough to the Sun that the ice vaporises to form an atmosphere, or coma, which may be blown by the solar wind to produce a visible tail. Or Comets Are The bright "star-like", objects with along tail, approaching the sun in highly elliptical orbit are called comets.
The bright star-like objects is commonly called the "head of the comet". It consists of frozen water, along with the sun, the ice and the gases along with dust change to form gaseous matter, which appear in the form of long tail. The tail of a comet always points away from the sun,because of the pressure of solar radiations (solar wind).The tail of the comets could be as long as 800 million kilometers.The time period of revolution of the comets around the sun is very long. There Are some comets which appear after fixed interval of time. Such comets are called periodic comets. Halley's Comet is one such periodic comet which is visible once in 76 years. It was sighted in 1910 and then in 1986. It is expected to visit us in the year 2062. Unlike planets, the comets do not last for ever in the solar system. It is because as they approach the sun, they lost a good amount of their mass in the form of gases and small chunks of rocks. At last they become smaller and smaller and finally disappear.
ASTRONOMY
All we learnt above is taken the branch of science called astronomy and one who studies it is called astronomer or astronaut. It is said that NICHOLAS COPERNICUS is THE FATHER OF MODERN ASTRONOMY (1543-1943).
HOW DO THE STARS EMIT LIGHT?
All stars are giant balls of hydrogen gas and this includes our sun which is a medium star. At the core (centre) of this giant hydrogen cloud, the temperature is usually from 2 million to 5 million degree celsius, the hydrogen gas fuses (joins or melts) to form a heavier gas called helium, at that temperature with the liberation of a huge amount of heat and light energy and it is this fusion of hydrogen gas within the core of the star which emits light energy.
THE SUN
The sun is the nearest star from the earth. Our sun is a medium order star in terms of its mass and brightness. You may wonder as to why the sun does not appear like the other stars or why does it appear bigger and hotter than other stars in the sky? Stars are always moving away from each other at a very high speed.But when viewed from the earth, the distance between them does not seem to change, because they are very far away from us. Hence, any change in the distance between them not become perceptible in few hun years.
WHY DO THE STARS APPEAR FROM EAST TO WEST?
The earth rotates about its north-south axis from west to east. Thus due to relative motion, all heavenly bodies (stars, planets, moon), etc., appear to move from east to west.
HOW FAR IS THE NEAREST STAR ALPHA CENTAURI, FROM THE EARTH.
The distance of the sun from the earth is 150 million kilometers. Whereas the distance of the nearest star (after sun) from the earth (Alpha Centauri) is 40678000 million kilometers. It is on account of these enormous distance that stars appear very small and appear to have much less heat and light as compared to the sun.
HOW BIG IS THE SUN AS COMPARED TO EARTH?
The diameter of the sun is 1,400,000 km (approx). This diameter is 109 times the diameter of the earth. Thus sun is approximately 300,000 times heavier than the earth.
WHAT ARE UNITS OF MEASURING THE DISTANCE OF STARS FROM THE EARTH?
Most of the stars are so far away from the earth, that even the light which travel at a speed of 3 x 10³ km/s (300,000 km/s) takes million of years to reach on the earth. Thus, the distances of the stars are measured in light years.
WHAT IS A LIGHT YEAR?
The distance travelled by the light at a speed of 300,000 km/s in one year (365 days) is called light year.
1 light year speed of light x 365 days
= 300,000 km/s x 365x24x60x60s
=9,460,000,000,000 km
= 9.46 x 10¹km
WHAT IS A LIGHT MINUTE?
The distance travelled by the light at a speed of 300,000 km/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
= 18,000,000 km=18x 10⁰km
HOW FAR IS THE NEAREST STAR ALPHA CENTAURI, FROM THE EARTH IN KILOMETERS
Alpha Centauri is at a distance of 4.3 light years.
Therefore, Distance in kilometer – Distance travelled in one light year x Number of light years
= 9.46 x 10¹² km/light year x 4.3 light
=40.678 x 10¹km.
WHY DO THE STARS APPEAR TO US LIKE POINT OBJECTS?
The stars, much like our sun are celestial bodies, which continuously emit heat and light. Our sun is a medium sized star but It appears bigger to us, because it is nearest to the earth. All the stars appear to us like points, because they are very far away from the earth. Most of the stars are so much far away, that the light from them takes million of years to reach the earth. Appeared to be changed the distance between any two stars not change when viewed from the earth?
Stars are always moving away from each other at a very high speed but when viewed from the earth, the distance between them does not seem to change, because they are very far away from us. Hence, any change in the distance between them does not become perceptible in few hundreds of years.
WHY DO THE STARS APPEAR TO MOVE FROM EAST TO WEST?
It is because the earth rotates about its north-south axis from west to east. Thus due to relative motion, all heavenly bodies (stars, planets, moon), etc., appear to move from east to west.
WHY DOES THE POLE STAR (POLARLS OR DHRUVA TARA) NOT CHANGE ITS POSITION IN THE SKY?
The direction of the Pole star is situated which is directly above the geographic north-pole of the earth's axis. Therefore the position relative to the earth does change and hence, it appears stationary.
CONSTELLATIONS
A group of stars which forms a recognisable pattern or shape is called a constellation. Astronomers have divided the whole sky into 88 constellations. Each constellation is assigned a name object to which it closely resembles. In ancient Indian astronomy, the constellations were known as Nakashatras. A few of the prominent constellations are discussed below.
(1) Ursa Major or Big Dipper or Vrihat Saptarishi
This constellation consists of 7 bright stars arranged in a pattern somewhat resembling the shape of a big bear. The stars marked 1, 2, 3 and 4 represent the body and the stars marked 5, 6, and 7 represent the tail of the big bear. The head and paws of the big bear are formed by some faint stars, not shown in diagram. Ursa Major The Ursa Major constellation can be linked to the following objects:
(i) It looks like an oversized ladle in which stars marked 1, 2, 3, and 4 form the cup of the ladle and stars marked 5,6 and 7 form the handle. The stars 1 and 2 at the end of the cup of the ladle are called pointer stars, as they point in the direction of the pole star.
(ii) It looks like a question mark suspended across the sky, where the stars 1, 2, 3 and 4 form the curved path and the stars 5,6, and 7 straight line part of the question mark.
(iii) It resembles a kite having a long tail. The Ursa Major is visible clearly in the northern part of the sky in the summer months, between April to September.
(2) Ursa Minor or Laghu Saptarishi or Dhruva Matsaya
Ursa Minor constellation is also a group of seven stars, similar to that of Ursa Major. However, the stars in Ursa Minor are closer and dimmer as compared to the stars of Ursa Major and They form an outline of a kite or a ladle. At the tail of Ursa Minor is a star of average brightness. It is called pole star or polaris. In Indian astronomy, the pole star is called Dhruva Tara. Ursa Minor is clearly
seen in northern sky in July in summer. Ursa major Polaris or Pole star Pointer stars
Relative Positions of Ursa Major and Ursa Minor.
How to locate the pole star?
Look straight in the direction of the stars situated at the far end of the ladle in Ursa Major (stars 1 and 2) and The star of medium brightness in the direction of the above stars is the pole star . These stars star 1 and 2 in Ursa Major which point in the direction of the pole star are called pointer stars.
(3) Orion or Hunter or Mriga or Vyadha
Orion is another constellation of 7 stars and is one of the most magnificent constellations in the winter sky. Its name in Indian astronomy is Vyadha or Mriga. It looks like a hunter with his shield and club upraised. The seven major stars in it form the body of the hunter. The head and limbs are formed by faint stars.
PHASES OF THE MOON
The moon is a non-luminous body. It has no light of its own and It only reflects the light of the sun falling on its surface. This reflected light reaches the earth and we see the moon. The part of the moon which is visible, is that reflects the sunlight towards the earth.The New Moon day, the moon is between the sun and the earth and the reflected light from the moon does not reach the earth
and hence it is not visible, In a way, the dark side of the moon is facing us on New Moon day. But The night, just after the new moon day, we see the crescent Moon. It is because only the reflected light from the crescent part reaches the earth and The rest of the moon is only faintly visible, because the sunlight reflected from the earth also falls on the moon's disc.
The crescent goes on increasing every day, till on the fifteenth day (from the New Moon day), the full bright face of the moon is visible but The earth is between the sun and the moon, such that
the night side of the earth is facing the day side of the moon. This is called Full Moon day. This gradual increase every day in the bright disc of the moon is called waxing of the moon.
The bright face of the moon goes on decreasing every night After the Full Moon and this decrease in the bright disc of the moon is called waning of the moon. By another fifteen days, New Moon is formed. This waxing and waning of the disc of the moon, as the moon revolves around the earth is called phases of the moon. The moon revolves around the earth. As the earth moves around the sun, in the same way the moon revolves around the sun, along with the earth. The moon completes one revolution around the earth in 271 days. It takes exactly the same time to spin once about the axis. Due to the same time for rotation on its axis and revolution around the earth, it always presents the same face towards the earth. However, as the moon revolves around the earth, the earth moves ahead in its own orbit around the sun. Thus, from the earth the moon appears to complete one revolution between one New Moon to next Moon in 291 ½ days. Lunar calendars
commonly used by astrologers are based on the fact that the Moon completes one revolution around the Earth in 29.5 days.
TEST YOURSELF
1. Define celestial bodies? Name any three celestial bodies.
2. Why do you classify the sun as a star?
3. Why do the stars appear like point objects?
4. What is a constellation? How does the constellation differ from a star?
5. what is the name a star which appears stationary from the earth. In which constellation is it situated?
6. What is "a light minute?" How many light minutes is the earth from the sun? Express this distance in kilometers?
7. How much time is involved from one new moon to another new moon as seen from the surface of the earth?
8. In how much time does the moon complete one rotation about its own axis?
PLANETS
A solid heavenly body which revolves around the sun in a well defined orbit is called planet. If you carefully look at the clear night sky, you will find some objects which (i) appear bigger and brighter than the stars (ii) they do not twinkle (iii) they change their position with respect to the other stars.
These bright objects are planets, which means wanderers, as they change their position in the night sky. There are nine planets in all, including the earth. They have no light of their own, but appear to shine as the sunlight from their surface is reflected. All planets (except Venus) rotate from the west
to the east. Due to different speeds of planets the position of them with respect to the earth changes every day. these planets are called Graha In Indian astronomy, all planets revolves around the sun. The list of all the planets in the order of increasing distance from the sun is given below, along with their Hindi names
Name of Planet. (in English). | Name of Planet (in Hindi) |
1. Mercury 2. Venus 3. Earth 4. Mars. 5. Jupiter 6. Saturn 7. Uranus. 8.Neptune 9. Pluto | Budha Shukra Prithvi Mangal Brihaspati Shani Indra or Arun Varun Yama |
THE SOLAR SYSTEM
Sun is the nearest star for us on the earth. It is believed that the sun was born 5 billion years (500 crore years) ago. It has been emitting a huge amount of heat and light and is expected to do the same for another 5 billion years. The sun along with the nine planets and their moons constitutes the solar system moreover In addition to the planets and their moons, other heavenly bodies have been found to revolve around the sun. They are asteroids, comets and meteors. Let us study more about them.
ASTEROIDS
The small piece of rocks or metal which revolve around the sun, in between the orbits of the mars and jupiter asteroids (meaning star like or minor planets). Asteroids are not visible to the unaided eye, but can be easily seen through a powerful telescope. They are of different sizes, the largest being Ceres, which is 633 km in diameter. It is estimated that there are around 100,000 asteroids. Each asteroid has its own orbit. Actually the orbits of asteroids are spread over a large distance forming a band. There are two schools of thought in formation of asteroids.
1. According to one school, these are original rocks and the metal chunks, which failed to form a planet, when other planets were formed in the solar system.
2. According to the second school of thought, they are the debris of a planet which collided with a moon of the Jupiter.
FOLLOWING WERE THE DECISIONS OF THE GENERAL ASSEMBLY OF IAU ON 23RD AUGUST 2006.
1. A planet is a body in near circular orbit around a star (in our case sun), which is big enough for the force of gravity to make it round and should not take more than 2 centuries to revolve around the Sun.
2. planet Pluto takes 248 years to revolve around the Sun, so it is disqualified as a planet.
3. Now Scientifically the Pluto and objects beyond it are called 'plutons', new members of solar family. The order of plutons is (1) pluto (ii) charon, (iii) 2003 UB,19-From August 2006 onward:
(i) There are eight planets revolving around the Sun.
(ii) There are three plutons revolving around the Sun, beyond neptune, in highly tilted orbits.
(iii) Mercury is the nearest planet from the Sun.
(iv) Neptune is the farthest planet from the Sun.
(v) Pluto is the first member of plutons.
(vi) Next to pluto is charon and finally 2003 UB-
(vii) Plutons have highly tilted orbit and take more than 200 years to revolve around the Sun.
TEST YOURSELF
1. What is a planet? How many planets revolve around the Sun?
2. Name the planet which (I) is nearest to the sun (ii) is farthest from the Sun (ii) supports life?
3. Name the planet which (i) revolves around the sun from east to west (ii) intersects the orbit of another planet?
4. Name one planet that was predicted before its discovery?
5. Name the planet having (i) largest number of moons (II) a system of number of rings?
6. What is the solar system? Name all the planets of solar system in the increasing order of distance from the sun ?
JKBOSE TEXTBOOK QUESTIONS
Choose the correct answer in Questions 1-3.
Question 1. Which of the following is NOT a member of the solar system?
(a) An asteroid (b) A satellite
(c) A constellation (d) A comet
Answer: (c) A constellation
Question 2. Which of the following is NOT a planet of the sun?
(a) Sirius (b) Mercury (c) Saturn (d) Earth
Answer: (a) Sirius
Question 3. Phases of the moon occur because
(a) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the Earth covers only a part of the moon’s surface.
(d) the thickness of the moon’s atmosphere is not constant.
Answer: (a) we can see only that part of the moon which reflects light towards us.
Question 4. Fill in the blanks.
(a) The planet which is farthest from the Sun is _____
(b) The planet which appears reddish in colour is ______
(c) A group of stars that appear to form a pattern in the sky is known as a _____
(d) A celestial body that revolves around a planet is known as ______
(e) Shooting stars are actually not _____
(f) Asteroids are found between the orbits of and ______
Answer: (a) Neptune (b) Mars (c) constellation (d) satellite (e) stars (f) Mars, Jupiter
Question 5. Mark the following statements as true (T) or false (F).
(a) Pole star is a member of the solar system.
(b) Mercury is the smallest planet of the solar system.
(c) Uranus is the farthest planet in the solar system.
(d) INSAT is an artificial satellite.
(e) There are nine planets in the solar system.
(f) Constellation Orion can be seen only with a telescope.
Answer: (a) False (b) True (c) False (d) True (e) False (f) False
Question 6. Match items in column A with one or more items in column B.
Answer: (i) (e) (g) (ii) (a) (iii) (c) (f) (iv) (d)
Question 7. In which part of the sky can you find Venus if it is visible as an evening star?
Answer: In west side of the sky.
Question 8. Name the largest planet of the solar system.
Answer: Jupiter
Question 9. What is a constellation? Name any two constellations.
Answer: A group of stars which has a recognizable shape is called a constellation.
Example: Ursa Major, Orion
Question 10. Draw sketches to show the relative positions of prominent stars in
(i) Ursa Major and
(ii) Orion
Answer: (i) Ursa Major (ii) Orion
Question 11. Name two objects other than planets which are members of the solar system.
Answer: Comets and asteroids.
Question 12. Explain how you can locate the Pole star with the help of Ursa Major.
Answer: Pole star can be located with the help of two stars at the end of Ursa Major. Imagine a straight line passing through these stars. Extend the imaginary line in North direction. This line is about five times the distance between two stars. A star is seen in this direction which is called Pole star.
Question 13. Do all the stars in the sky move? Explain.
Answer: No, all the stars do not move in the sky. Due to the rotation of the Earth on its own axis stars seem to move in the sky.
Question 14. Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?
Answer: The stars are very far away from the Earth and it is not convenient to express such distances in kilo¬metres. Thus, such large distances are expressed in unit known as light year.
If we say that a star is eight light years away from Earth, it means that the light from star will reach the Earth in eight years.
Question 15. The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accommodate?
Answer:
Let the radius of Earth be r units.
Question 16. Boojho made the following sketch (Fig. 17.6) of the solar system. Is the sketch correct or not, correct it.
Answer:
No, the sketch made by Boojho is not correct. The correct sketch is given below:
Activity 1
Observe the moon continuously for several nights, preferably from one full moon to the next. Make a sketch of the moon every night in your notebook and note the day from the day of the full moon. Also, note every day the part of the sky (east or west) in which the moon is seen.
Solution:
We find that there is a change in the shape of the moon every day and the moon appears to be perfectly round on the full moon day. On the fifteenth day of the month, we see that the moon is not visible even if the sky is clear.
Thus, the moon goes on increasing every day, till on the fifteenth day and the full face of the moon is visible. After the full moon the bright part of the moon goes on decreasing every night and by another fifteen days again new moon is formed.
Activity 2
Take a big ball ora pitcher. Paint half of it white and half black.
Go out into the playground with two of your friends. Draw a circle of radius of about 2 m on the ground. Divide the circle into eight equal parts as shown in Fig. 17.1.
Stand at the centre of the circle. Ask a friend to hold the ball at different points of the circle. Ask her to keep the white portion of the ball always towards the Sun. If you are performing this activity in the morning then the white portion of the ball should be kept towards the east. If the activity is being performed in the afternoon then the white portion of the ball should be kept towards the west. In each case the line dividing the white and black portions is kept vertical.
Standing at the centre of the circle observe the visible white portion of the ball while your friend stands at the points on the circle marked earlier. Draw the shape of the white portion as you see it. Compare your drawings with the different phases of the moon as shown in Fig. 17.8.
Solution:
Do it yourself.
Activity 3
Draw a circle of about 1 m diameter on the ground. Ask one of your friends to stand at the centre of this circle. You revolve around your friend in such a manner that your face always remains towards him. Can your friend see your back? How many rotations did you complete in one revolution? The moon revolves around the Earth in a similar manner.
Solution:
No, my friend cannot see my back. One rotation is completed in one revolution.
It is concluded that the moon completes one rotation on its axis as it completes one revolution around the Earth.
Activity 4
Stand in the centre of a big room and start rotating. In which direction will the objects in the room appear to move? Do you see them moving in the direction opposite to your motion?
Solution:
The object appear to move in the opposite direction to our motion.
Activity 5
Go out into the playground with four or five of your friends. Draw four circles of radii 1 m, 1.8 m, 2.5 m and 3.8 m, all having a common centre (Fig. 17.5).
Ask one of your friends to stand in the centre and represent the Sun. Your other four friends may represent Mercury, Venus, Earth and Mars.
Ask your friends to move around the Sun in anti-clockwise direction in their own orbits (Fig. 17.5). Do they collide with one another?
Solution:
No, they do not collide with one another, because they have fixed orbits of their own. In a similar way, planets move in their own orbits.
Questions and Answers
Question 1. Name the instrument you will use to observe rings of the planet Saturn.
Answer: Telescope.
Question 2. Which star appears to remain fixed to us ? What is / are the name/s given to it ?
Answer: Pole star appears to be fixed. Its name is Dhruv Tara.
Question 3. Planet ………….. is known to have the largest number of natural satellites.
Answer:Jupiter.
Question 4. Name any two constellations that have seven prominent stars in them.
Answer: Ursa Major and Ursa Minor have seven prominent stars in them.
Question 5. Name the planet that was predicted before it was actually observed.
Answer: Pluto
Question 6. Why the stars are not visible during the day ?
Answer: The stars are not visible during the day because of the glare of bright sunlight.
Question 7. Which of the following is NOT a member of the solar system ?
An asteroid A satellite A constellation A comet
Answer: A satellite.
Question 8. Match the items in column I with one or more items in column II
Column-I | Column-II |
(a) Star | (i) Saturn |
(b) Constellation | (ii) Pole star |
(c) Planet | (iii) Great Bear |
(d) Satellite of the earth | (iv) Moon |
(v) Earth | |
(vi) Orion | |
(vii) Mars |
Answer:
Column-I | Column-II |
(a) Star | (i) Pole star |
Question 9. In which part of the sky can you find Venus if it is visible as an evening star ? [JKBOSE]
Answer: Venus appears in the western sky as an evening star.
Question 10. What is full moon day ?
Answer: The day on which the whole disc of the moon is visible is known as the full moon day.
Question 11. Can you see the back side of the moon from the earth ?
Answer: No, we cannot see the back side of the moon from the earth.
Question 13. Does the moon have atmosphere and water ?
Answer: No, moon doesn’t have atmosphere or Water.
Question 14. Can you hear sound on the moon ?
Answer: No, we cannot hear sound on the moon because there is no medium in which sound can travel.
Question 15. What is an orbit ?
Answer: The path taken by planets to revolve around the sun is called an orbit.
Question 16. Why do the planets not collide while revolving around the sun ?
Answer: Planets move in their own orbits, so they don’t collide with each other.
Question 17. Is the earth a satellite of the sun ?
Answer: No, even though the earth revolves around the sun but it is not a satellite of the sun, because satellites revolve around the planets.
Question 18. Why is it difficult to observe Mercury ?
Answer: Mercury is closest to the sun, so it is hidden by the glare of the sun. So, it cannot be seen.
Question 19. Name two planets having no satellites.
Answer: Mercury and Venus.
Question 20. What are meteor showers ?
Answer: When the earth crosses the tail of the comet, swarms of meteors are seen, known as meteor showers.
Question 22. What is meant by remote sensing ?
Answer: Collecting information from a distance by satellites is known as remote sensing.
Question 23. Name any three celestial bodies.
Answer: The stars, Sun and Moon are celestial bodies.
Question 24. Why do we classify the Sim as a star ?
Answer: The Sun is a star because it continuously emits light and heat. It appears large as compared to other stars because it is nearer to the Earth.
Question 26. Name the planets that were known to ancient astronomers.
Answer: The planets known to ancient astronomers were Mercury, Venus, Earth, Mars, Jupiter and Saturn.
Question 27. The artificial satellites are used for ………., ……., ……….. and …………
Answer: Long distance communication, research, remote sensing and defence.
Question 28. Which of the following is a star ?
Alpha Centuari Diebos Orion Phobos
Answer: Alpha Centuari.
Question 29. Ursa Major is a star, seen only with a telescope,a constellation, a natural satellite of Mars
Answer: a constellation.
Question 30. The stone like objects entering the Earth’s atmosphere appear as …………. of …………. at night and these are called …………
Answer: Streak, light, meteors.
Question 31. A celestial body that appears to change its position with respect to the stars is called ………….
Answer: Earth.
Question 32. Which planet is nearest to the Earth ?
Answer: Venus.
Question 33. Name two planets which are near to the Sun.
Answer: Mercury and Venus.
Question 34. Which planet moves in a different plane ?
Answer: Pluto.
Question 35. Which planet of the solar system is the hottest ?
Answer: Venus.
Question 36. What are asteroids ?
Answer: They are very small planets of rock and metal which revolve around Sun mainly between Mars and Jupiter.
Question 37. Name the branch of science which deals with the study of the universe.
Answer: Astronomy.
Question 38. What is the shape of the Earth ?
Answer: The Earth is not a perfect sphere, but is somewhat flattened at the poles and is bulging at the equator.
Question 39. What is solar system ?
Answer:The sun and the nine planets along with their natural satellites constitute the solar system.
Question 40. What are meteorites ?
Answer: A part of meteor which fails to bum in Earth’s atmosphere and reaches the surface of Earth is called meteorite.
Question 41. Name the comet, which reappears after 76 years.
Answer: Halley’s comet.
Question 42. Give the other name of meteors.
Answer: Shooting stars.
Question 43. Why does the sun not appear like other stars ?
Answer: The sun appears bigger and hotter as compared to other stars because it is very close to the Earth.
Question 44. What is atmosphere ?
Answer: The Earth is surrounded by an envelope of air known as atmosphere.
Question 45. Name the galaxy in which our solar system is situated.
Answer: Milky way.
Question 46. How many galaxies are there in the universe ?
Answer: Hundred billion galaxies.
Question 47. How many stars are present in each galaxy ?
Answer: Each galaxy consists of 100 billion stars.
Question 48. Name the astronauts who landed on the Moon in 1969.
Answer: Niel Armstrong and Edwin Aldrin.
Questions and Answers
Question 1. Mention any two differences between natural and artificial satellites.
Answer:
Natural Satellite | Artificial Satellite |
(i) A celestial body revolving around a planet is called a natural satellite. | (i) A man-made satellite revolving around the Earth is called an artificial satellite. |
Question 2. How is the tail of a comet formed ?
Answer: When a comet comes near the sun, some of its ice turns into gas. Gas and loose dust, freed from ice create a long illuminating tail behind it.
Question 3. Venus is hotter than mercury, though it is farther away from Sun. Why ? [DAV2008, 06]
Answer: Venus contains a higher percentage of carbon dioxide. So, the greenhouse effect is more by the trapping of the infrared rays of the sun.
Question 4. Define light year. What is the relation between light year and kilometers ? [ATS 2007]
Answer: One light year is the distance travelled by light in one year.
1 light year = 9.46 * 1012 km.
Question 5. Give any two points of difference between comets and meteors. [DAV2007]
Answer:
Comets | Meteors |
(i) Comets are heavenly bodies which revolve around the sun in an elliptical path. | (i) Meteors are pieces of rocks floaing in space which get heated up on entering into earth’s atmostphere. |
MCQs
Question 1. Out of the following, the only one that is a Galaxy, is
(a) Alpha centuari (b) Jupiter
(c) Halley’s comet (d) The Milky Way
Answer: (d)
Question 2. The constellation, of which pole star is a part, is
(a) Ursa Major (b) Ursa Minor
(c) Orion (d) Scorpio
Answer: (b)
Question 3. The large number of rocky objects, that lie between the orbits of Mars and Jupiter, are known as
(a) Comets (b) Asteroids (c) Meteorites d) Meteors
Answer: (b)
Question 4. The largest planet in the solar system is
(a) Neptune (b) Earth
(c) Jupiter (d) Uranus
Answer: (c)
Question 5. Which one of the following is better known as morning and evening star ?
(a) Neptune (b) Mercury
(c) Proxima centauri (d) Venus
Answer: (d)
Class 8 Science Chapter 1
Microorganisms: Friends and Foe
This chapter manages destructive and valuable kinds of microbes and their significance in different areas. The places where microorganisms live, microorganisms and us, harmful microorganisms, food preservation, nitrogen fixation, and nitrogen cycle are a portion of the primary topics covered in this chapter.
Class 8 Science Chapter 2
Class 8 Science Chapter 3
Conservation of Plants and Animals
Conservation of plants and animals is a critical subject of science. This part will push the students to not just to understand the human exercise that negatively affects the nature’s abundance yet in addition to manners by which they can ensure the fauna and flora of the ecosystem.
Class 8 Science Chapter 4
Class 8 Science Chapter 5
Class 8 Science Chapter 6
Food Production and Management
This chapter explains rural practices related to the creation of yield and their administration.It includes the presentation of various harvest, their climatic and nourishing necessities and the preparation of soil for comprehensive improvement of the crops
Class 8 Science Chapter 7
Class 8 Science Chapter 8
Class 8 Science Chapter 9
Class 8 Science Chapter 10
Reaching the Age of Adolescence
In this chapter, the student will find out about changed that happen in the human body after which an individual ends up fitting for reproduction.in this chapter we will learn about the human conceptive organs and the role of hormones in the development of an individual.
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