Imagine that Bob, at a spaceport, observes Alice flying by to the right in her spaceship at a velocity of 0.9c. When Alice’s ship had been previously docked at the spaceport, Alice had measured its length as 100 meters. Alice has five clocks on her spaceship: one in front (at 0 meters), one at 25 meters, one at 50 meters, one at 75 meters, and one at the rear at 100 meters. All the clocks are synchronized in Alice’s frame of reference. When Alice flies by Bob, Bob uses his lattice of synchronized clocks to take simultaneous photos of Alice’s clocks (simultaneous in Bob’s frame of reference). Bob compares the times shown in the photos of Alice’s second clock (at 25 meters) and fourth clock (at 75 meters). Which clock is running ahead of the other?