A news story is making the rounds that the star T Pyxidis may well one day go supernova. Cool, the story agrees, but its distance is much, much closer to us than we realized, and frankly, things would get really bad, really fast here on Earth.
Okay, so the star is 3,300 light years away, right? Right, but if it blew up 3,299.9 years ago, the first youd know about it was when it killed you in a few days.
Not quite, as you expect.
The Bad Astronomer knows a bit about this, and explains that it would need to be closer than 25 light years away to be even a remote threat to us. A Type 1a supernova might potentially be an impressive visual display 3,300 light years away, but the explosion itself wont even put a ripple on a dandelion here on Earth.
So cheer up. The Mandarin is working on something much scarier only a few miles from your house.