In astronomical calculations, the term light-year is used very often. The light-year stands for:
- AThe time the Earth takes to complete one revolution around the Sun
- BThe time sunlight takes to reach the Earth
- CThe distance that light travels in a year
- DNone of the above
Show answer and explanation
Correct answer: (c) The distance that light travels in a year
Explanation
A light-year is a unit of distance, not of time. It is the distance light travels in a vacuum in one year:
- about 3 × 10⁸ m/s × 3.15 × 10⁷ s ≈ 9.46 × 10¹² km.
It is used for the huge distances between stars. The nearest star after the Sun, Proxima Centauri, is about 4.2 light-years away. Sunlight takes about 8 minutes 20 seconds to reach the Earth.