If a supernova were to go off somewhere in our galaxy, the minimum safe distance for Earthbound life would be about 50 light years.  Any closer than that, and we would experience an intense blast of high energy radiation and an eventual shower of radioactive particles.  It would be like nuclear bombs were set off all around the Earth, causing little destruction but a lot of radioactive fallout.  Supernovae are incredibly powerful to be able to cause such damage at 50 light years, but even at larger distances, we can see evidence of their effects here on Earth. A team of...