… were a supernova to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions. X-rays and more energetic gamma-rays from the supernova could destroy the ozone layer that protects us from solar ultraviolet rays. It also could ionize nitrogen and oxygen in the atmosphere, leading to the formation of large amounts of smog-like nitrous oxide in the atmosphere.
The nearest Type 2 supernova candidate is Betelgeuse, 430 light-years away. It will be spectacular when it does go boom, but it will probably be harmless. This could have happened 429 years ago and we’d learn about it this year. Or it might be a million years from now. Nobody knows.
Type 1 supernova, however, is caused when a white dwarf accretes hydrogen fuel from a binary partner, when the fuel reaches a certain level of pressure it fuses all at once in a brilliant explosion. There are a lot of white dwarf stars inside of 100 light-years. But the chance of it happening in our lifetimes is probably less than being killed by a falling meteorite.
The reason I mention all of this is in Book 5 and beyond. I get to research some very interesting things.