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CBSE NCERT Solutions for Class 8 Science Chapter 17:
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?
The distance of the stars from the Earth and the distance between the stars are
very large. It is inconvenient to express these distances in kilometer (km). Thus, these large distances are expressed in light years. One light year is the distance travelled by light in one year. One light year is equal to 9.46 x 10^12km.
A star is located eight light years away from the Earth. This means that the distance between the star and the Earth is equivalent to the distance travelled by light in eight years,
i.e., a star is located
8 x (9.46 x 10^12) = 7.6 x 10^13km away from the Earth.
Explain how you can locate the Pole Star with the help of Ursa Major.
The pole star can be located using the ursa major constellation, by imagining a
line towards the Northern direction connecting two stars presnt at the end of the bowl, This imaginary line meets Pole Star. The length of the imaginary line from the bowl is about five times the distance between the two stars of the bowl.
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.
Option A: we can see only that part of the moon which reflects light towards us.