Download Chapter 17 Science Class 8

Chapter 17 Science Class 8 2016
CHAPTER 17
STARS AND THE SOLAR SYSTEM
Summary of main points in the Chapter
4. The Moon and Venus appear to
change phases, because from Earth
only part of the reflected sunlight can
be seen as these two move in their
orbit.
The Earth has many man made or
artificial satellites that are nearer than
the Moon , and therefore, do not
reflect sunlight regularly. They can
seen for a few seconds, occasionally
, moving very fast .
1. Stars are celestial bodies that emit
light of their own. Groups of stars
that form a shape is a Constellation.
Distance from stars is measured in
Light Years. The stars appear to move
from East to West, just like the Sun,
that appears to rise in the East and set
in the West. The Pole Star does not
seem to move because it is near the
angle of Earth's axis. Therefore, it is
always seen the the North, near the
Big Dipper or Sapt Rishi
Sun is a star
3. The Outer Planets include Jupiter, as the
largest and fifth planet, Saturn with Rings as
sixth, Uranus and Nepture at number seven
and eight. The planets have smaller bodies
revolving around them.
These are Satellites . The Earth has only one
natural satellite, Mars has two, Jupiter has
four large and 12 small , Saturn has 1 large
and 15 small, Uranus has 5, and Neptune
has 2 satellites.
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2. From Earth, the Sun is the nearest
star . It has eight Planets revolving
around it. These 8 planets, asteroids,
meteors, comets form the Solar
System. Earth is the third planet , the
first is Mercury, and second is Venus.
Fourth planet is Mars. These 4 are
'Inner Planets' in the Solar System
After Mars is an Asteroid belt
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Chapter 17 Science Class 8 2016
Exercises on page 236
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.
Correct answer is (c)
2. Which of the following is not a planet of the sun
a) Sirius
b) Mercury
c) Saturn
d) Earth
Correct answer is (a)
3. Phases of the moon occur because
a) We can see only that part of the moon which reflects light towards
the Earth
b) Our distance from the moon keeps changing
c) The shadow of the Earth covers only a part of moon’s surface.
d) The thickness of moon’s atmosphere is not constant
Correct answer is (a)
4. Fill in the blanks
a) The planet which is farthest from the Sun is Neptune
b) The planet which appears reddish in colour is Mars.
c) A group of stars that appear to form a pattern in the sky is known as
a constellation
d) A celestial body that revolves around a planet is known as a satellite.
e) Shooting stars are actually not stars.
f) Asteroids are found between the orbits of Mars and Jupiter.
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Chapter 17 Science Class 8 2016
5. Mark the following statement as true (T) or false (F)
a) Pole Star is a member of the solar system
(F)
b) Mercury is the smallest planet of the solar system
(T)
c) Uranus is the farthest planet in the solar system
(F)
d) INSAT is an artificial satellite
(T)
e) There are nine planets in the solar system
(F)
f) Constellation Orion can be seen only with a telescope ( F)
6. Match items in column A with one or more items in column
A
1
2
3
Inner planets
Outer planets
Constellation
4
Satellite of the Earth
B
Earth and Mars
Saturn
Great Bear or the Big Dipper or
Ursa Major, and Orion
Moon
7. In which part of the sky can you find Venus if it is visible as an evening
star?
Answer. As an evening star, Venus is visible in the western part of the
sky.
8. Name the largest planet of the solar system
Answer. The largest planet of the solar system is Jupiter.
9. What is a constellation? Name any two constellations.
Answer. A constellation is a group of many stars in which the brighter
ones make a pattern in the sky.
10.Name two objects other than planets which are members of the solar
system
Answer. Comets and meteors , and the asteroid belt between Mars and
Jupiter are also members of the solar system.
11.Do all the stars in the sky move? Explain.
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Chapter 17 Science Class 8 2016
Answer. Yes, all stars move in the sky and their movement appears to be
from east to west.
12.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 Universe with millions of galaxies is so vast that speed of
light is the better unit to measure distances in space because it is the
fastest. Light travels in vacuum with an enormous speed of 3×108 m s-1.
This means it travels at a speed of 300,000 km per second. One light year
is the distance the light travels at this speed from a star to earth.
When we say that a star is eight light years away from the earth, it
means that the light from that star started its journey eight years ago from
the time it reached earth.
From Earth, the Sun which is the nearest star. Its distance from
earth is 8 (eight) light Minutes. This means that the light that is seen by
us on earth at Sunrise, is eight minutes older from the time it actually
started from the sun. In other words, the sun comes on the horizon or it
‘rises’, eight minutes before, we see the sunrise. It actually sets eight
minutes before we see the sunset on the horizon.
13. 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
adjusted inside Jupiter?
Answer. 130 earths can be adjusted inside Jupiter.
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