Ncert Exercises & Solutions

The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?

Time taken by quasar light to reach Earth = 3 billion years = 3 × $10^{9}$ years

= 3 × $10^{9}$ × 365 × 24 × 60 × 60 s

Speed of light = 3 × $10^{8}$ m/s

Distance between the Earth and quasar

= $(3 \times 10^{8}) \times (3 \times 10^{9} \times 365 \times 24 \times 60 \times 60)$

= 283824 × $10^{20}$ m = 2.8 × $10^{22}$

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