Things in space being “xxxx lightyears away”, therefore light from the object would take “xxxx years to reach us on earth”

Question

I don’t really understand it, could someone explain in basic terms?

Are we saying if a star is 120 million lightyears away, light from the star would take 120 million years to reach us? Meaning from the pov of time on earth, the light left the star when the earth was still in its Cretaceous period?

In: 292

Answer 1

When people invented miles they were to talk about things on earth scales. Something can be 5 miles away or 100 miles away and that is a number that makes sense. The nearest start is 55 trillion miles away 55,000,000,000,000. No one wants to write 55,000,000,000,000 miles over and over, so they decided to go with something good for space.

A light year is the number of miles light can travel in one year. The nearest star is 4.3 of those, and it’s back to a scale people can talk about easily.