UPSC NDA I 2019 General Ability Solved Paper

Concept:A light-year is a unit of length used to measure astronomical distances, not a unit of time.Explanation:The speed of light in vacuum is $3 \times 10^{8}$ m/s.One Julian year has $365.25$ days.Distance = speed × time = $3 \times 10^{8} \times 60 \times 60 \times 24 \times 365.25$ meters.This equals approximately $9.467 \times 10^{15}$ m.Thus a light-year is the distance light travels in one year.It is a unit of length, used for very large distances between stars and galaxies.The term "light-year" was introduced by Friedrich Bessel in 1838 after first accurate stellar distance measurement.Answer:Option A: very large distances.