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

Sometimes when you ask someone how far away the next city is, they’ll say something like “Oh it’s about 2 hours away” They’re making a mental shortcut by saying “it’s about 120 miles away and if the speed limit is 60mph, it will take about 2 hours.”

Scientists do the same time when discussing distances to far away stars or galaxies. When they say, “Oh it’s about 100 lightyears away.” what they’re really saying is, “It’s about 946,100,000,000,000,000 kilometers away, and if the speed of light is 9,461,000,000,000,000 km/year, the light will take 100 years to reach us.”