Example: Are the explosions simultaneous?
Simultaneous?
An experimenter in reference frame S stands at the origin looking in the
positive x-direction . At t = 3.0 \mu s she sees firecracker 1 explode at x = 600 m. A short time later, at t = 5.0 \mu s, she sees firecracker 2 explode at x = 1200 m. Are the two explosions simultaneous? If not, which firecracker exploded first?