I don’t know where they got that number from. It’s depending on a multitude of factors like, type of supernova and orientation of the supernova (like if we’re i

I don’t know where they got that number from. It’s depending on a multitude of factors like, type of supernova and orientation of the supernova (like if we’re in line for a gamma ray burst) *edit For anyone interested in this topic I suggest Phil Plait’s book in the subject