well the text book question is (transfer me over to hmwk help its ok) 2 Civilizations are evolving on oppposite sides of our galaxy (d = 10^5 ly) at time t = 0 in the galaxy frame of reference, civilization A launches its first intersteller spacecraft, 50,000 years later, measured in the galaxy frame, civilization B lunches its first spacecraft. a being from a more advanced civilization, C, is travelling through the galaxy at .99c on a line from A to B. Which civilaztion does C judge to have first achieved interstellar travel, and how much in advance of the other? the book given answer is as follows but how? C judge B 1st by 350,000 years well I assumed anyways that C would observe B because the light from B is going to get to him before the light from A gets to him seeing how it has to travel 10^5 ly s so how do i calc this?