Space questions, answered
What is a light-year?
A light-year is a distance, not a time — it's how far light travels in one year: about 9.46 trillion kilometres (5.88 trillion miles).
Because light is the fastest thing there is, a light-year is a convenient way to measure the enormous gaps between stars. The nearest star beyond the Sun, Proxima Centauri, is about 4.2 light-years away — meaning the light you see from it left more than four years ago.
This also makes telescopes into time machines: when we look at a galaxy a billion light-years away, we see it as it was a billion years ago, because that's how long its light took to reach us.
People also ask
Is a light-year a measure of time?
No — it's a measure of distance: the distance light covers in a year (~9.46 trillion km).
Sources: NASA — how far is a light-year