Supernova

A supernova is an explosion that results from the death of a star. Depending on the type of star, supernovas can eject different proportions of matter or radiation (including light). Most heavy elements in the universe are the products of supernovas.

When a supernova occurs within "close" range of a planet, it can have effects on that planet's environment, which is of greater concern now that humanity has spread across the galaxy. At the outer reaches--about 1000 light years away--the supernova will only contribute a little brightness in the sky. When closer, the incoming radiation heats the atmosphere by a few degrees.

Within about 30 light years, catastrophic damage can occur. Gamma radiation radiolyses the upper atmosphere, stripping away any kind of ozone layer and allowing harmful solar and cosmic radiation to bombard the surface. On planets without a strong magnetosphere or shielding, the gamma rays can be directly harmful to the biosphere.