You’re writing a galactic history involving two civilizations that evolve on opposite sides of a 1.0x10⁵ -ly-diameter galaxy. In the galaxy’s reference frame, civilization B launched its first spacecraft 45,000 years after civilization A. You and your readers, from a more advanced civilization, are traveling through the galaxy at 0.99c on a line from A to B. Which civilization do you record as having first achieved interstellar travel, and how much in advance of the other?