Question

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 1

Distance between stars are very large in magnitude. Hence a new unit is required so that the value of distance is not too big and is sensible. A light year is defined as the distance travelled by light in one year.

$1ly=9.461\times {10}^{12}km$

$8ly=7.57\times {10}^{13}km$

A star is eight light years away from earth means that light from the star takes 8 years to reach the earth's surface. As shown above, its approximate distance from the earth is $7.6\times {10}^{13}km$.