We receive a radio message from a civilization around a star about 40 lightyears from Earth? If we reply right away, how long will it be between the time THEY sent the message and the time they receive our reply?
A) 40 years
B) 80 years
C) 400 years
D) 20 years
E) it depends on the speed of the radio wave; so it can't be calculated from the information given

Question

Quizplus · Accepted Answer

Since the star is 40 lightyears away from Earth, it would take the radio signal 40 years to travel from the civilization to Earth. If we reply right away, it would take another 40 years for our radio signal to reach the civilization, resulting in a total travel time of 80 years.

We Receive a Radio Message from a Civilization Around a Star