On this day in 1604, Kepler’s Supernova was first observed. It wouldn’t be noticed by Johannes Kepler until a week later, but he observed it for a year and published a book about it. It’s an important event because it was the last time a supernova was observed in our galaxy. (We observe them in other galaxies.) And that’s really interesting if you consider that just 32 years earlier, Kepler’s colleague Tycho Brahe had observed another supernova. So two supernovas in a small span of time, and then nothing for over 400 years. But that’s the way random events are.
In general, a supernova would have to be closer than 100 light-years from the Earth to have an effect on us. Statistically, we should have one within 33 light-years every 250 million years. That’s one of the things about us being out here on the edge of the galaxy: it’s kind of boring. But it is probably also necessary for the development of advanced life. Further in, life on the Earth would have likely been destroyed before it got too far.
Kepler’s Supernova is thought to have been something on the order of 20,000 light years away. The one Brahe observed was less than half that distance. Still, these supernovas were far, far away — where they belong.