Extremely dangerous. A supernova explosion can give out more light in that instant of explosion than the Sun gives out in its entire lifetime. Such an explosion contains so much energy that the Earth will be destroyed if it is anywhere within a 50–70 light year radius of the explosion. read more
A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly less than 10 to 300 parsecs (30 to 1000 light-years) away[2]) to have noticeable effects on its biosphere. read more