Page 183 - Science Class 08
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As it is not easy to express such a long distance THE POLE STAR
in kilometers, so the unit used to express the You already know that our earth rotates about
distance between the objects of universe is its axis from west to east. However, this is an
‘light year’. imaginary axis, there is no such any line which
PLANETS is real. Because of this rota ons of the earth,
we feel that the stars are moving from east to
Planets are heavenly bodies that revolve
west.
around the sun. They do not have their own
But, there is one star that appears in the north-
light. However, their surface reflects sunlight.
hemisphere at a fixed posi on. This star is
Planets are smaller than stars. Our earth is also
known as Polaris or Pole Star or the Dhruv
a planet. There are eight planets in our solar
Tara.
system namely— Mercury, Venus, Earth, Mars,
The Pole Star, got its name from a Greek word
Jupiter, Saturn, Uranus and Neptune.
‘Polos’ which means ‘Pivot’. It looks at a fixed
Light Year posi on because this star is located at around
If you think driving across the na on to go to just that point where the axis of rota on of the
the beach takes a long me, try flying across earth meets (when produced) the imaginary
the universe! A light year is a unit of measure- celes al sphere.
ment that measures the distance light travels in In ancient me, it served as a direc on
a year. One light year is the distance covered indicator guide to help the navigator loca ng
by light in one year. Light rays travel at a speed direc on in the night.
of 300,000 km per second. CONSTELLATIONS
So, they cover a distance of about: We can see a definite and recognisable pa ern
of stars in the night sky. These pa erns formed
300,000 × 365 ¼ × 24 × 60 × 60 = 9, 460, 800
by the group of stars are called constella ons.
million kilometres or (about 9460 billion or
about 9.5 trillion kilometres) in one year. These stars in group or a constella on always
remain together in the same posi on and
The light of the sun takes 8 minutes and 19
shape.
seconds (8.3 minutes) to reach the earth. So,
The constella ons appears to move in the sky
the sun is about 8.3 light minutes away from us.
from west to east and the earth moves from
Proxima Centauri is the next nearest star a er west to east. The stars and constella ons
the sun. It is about 27,000 mes further away appear to move from east to west because they
from the earth than the sun. It is about change their posi ons. But, their shapes
38,000,000,000 km away from the earth. So, remain the same because the stars remain in
we can say that it is about 4.3 light years away the same posi on with respect to each other.
from the earth.
The brighter star, Sorus, is about 8.7 light years
away from the earth.
Betelgeuse, one of the largest known star is
520 light years away.
Science-8 183
