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

Light-Year

1. The distance between stars is very large and estimated to be in the millions of kilometers range.
2. The kilometer unit is inconvenient for describing such a big distance, therefore light-years are used instead.
3. One light-year is the distance traveled by light in one year and it is used to express large distances.

$1\text{light-year}=9.46x{10}^{12}\text{km}$

Interpretation of Eight Light-Years

1. If a star is eight light-years away from the Earth, the distance between them is equivalent to the distance traveled by light in eight years.
2. The statement that a star is eight light-years away from the Earth can be interpreted as follows:

$$\begin{gathered} \text{Distance}=8✕(9.46✕{10}^{12}) \\ \text{Distance}=7.6✕{10}^{13}\mathrm{km} \end{gathered}$$

Hence, the distance between stars is expressed in the light years as it is complicated to express the distance in kilometers and eight light years is the distance traveled by the light in eight years. The distance between the star and the Earth which is eight light-years away from the Earth is $7.6✕{10}^{13}\mathrm{km}$.