If Proxima Centuri (4 light years away) went supernova, what would it look like from Earth?
It would be one heck of a light show, and brighter than anything else in the sky other than the Sun. In fact, it would be apparent even in daylight. Most supernovae attain an absolute magnitude of at least -16, which means that at a distance of 4 light years it would be at least -19 in our skies. However, a supernova that close would be disastrous for us here on Earth. Extreme levels of radiation from the blast will sterilize or cause massive extinction events on any planet at distances to at least 30 light years for a conventional supernova that explodes in all directions. So we would see a brilliant spectacle in our sky, then find out the ozone layer’s toast and that we’ve been blinded by UV light from the Sun getting through to the ground unimpeded. It won’t help us also in that we also would get very harmful, even fatal doses of ionizing radiation. In any event, none of the stars that belong to the Alpha Centauri system are anywhere near the mass required to explode as a supernova.
