From David Bazley:

Re: Blast called furthest object visible to naked eye (March 20): Further to this most interesting article: I have always wondered what risk the earth is under from supernovas and Googled the subject - below is only part of one page.

How close would the average supnova have to be in order to be a threat or even to extinguish all life please? Are we talking 10 light years or 100 light years?