Question

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 ?

Answer 1

Given, the time it takes for quasar light to reach the Earth is 3 billion years and speed of light is 3× 10 8   ms -1 .

Let S be the distance between Earth and quasar, then

S= ct

Here, c is the speed of light and t is the time.

Substitute the values in the above equation.

S= ( 3× 10 8   ms -1 )( 3 billion years ) =( 3× 10 8   ms -1 )( 3× 10 9  years )( 365 days 1 year )( 24 hour 1 day )( 60 min 1 hour )( 60 s 1 min ) ≈2.8× 10 22  km

Hence, the distance in km of a quasar from which light takes 3.0 billion years to reach the Earth is 2.8× 10 22  km.