<snip> There is also an estimate that the Starfish atomic test from the early > '60's could be detected in X-ray emissions out 400 AU. Â I haven't done > the math but 400 AU is probably not all that far in light years. 400AU = .006 Light Years, or roughly 10x pluto's orbit - not even to the Oort Cloud 400AU is ABOUT 2 light-days (1 light-day = 173AU)