If we say that a galaxy has a lookback time of 1 billion years,we mean that
A)its light traveled through space for 1 billion years to reach us.
B)is now 1 billion light-years away.
C)it was 1 billion light-years away when the light left the galaxy.
D)it is 400 million years old.

Question

Quizplus · Accepted Answer

Lookback time refers to the amount of time it took for light from an object to reach us. Therefore, if a galaxy has a lookback time of 1 billion years, it means that it took 1 billion years for its light to travel through space and reach us.

If We Say That a Galaxy Has a Lookback Time