1. The problem statement, all variables and given/known data You and a group of female and male friends stand outdoors at dusk watching the Sun set and noticing the planet Venus in the same direction as the Sun. An alien ship lands beside you at the same instant that you see the Sun explode. The aliens admit that earlier they shot a laser flash at the Sun, which caused the explosion. They warn that the Sun's explosion emitted an immense pulse of particles that will blow away Earth's atmosphere. In confirmation, a short time after the aliens land you notice Venus suddenly change color. You and your friends plead with the aliens to take your group away from Earth in order to establish the human gene pool elsewhere. They agree. Describe the conditions under which your escape plan will succeed. Be specific and use numbers. Assume that the sun is 8 light-minutes from Earth and Venus is 2 light-minutes from Earth. 3. The attempt at a solution This has got me confused. If the exploding Sun emits planet-color-changing radiation when it explodes, wouldn't said radiation affect the Earth as soon as you can see the explosion? It's almost as if the problem is implying that the radiation is moving slower than c, which to my knowledge doesn't happen.