:
The Milky Way is approximately 100,000 light years across (diameter).
The last supernova explosion in our galaxy was sighted by Kepler in
1604. Of course the size of a supernova or a hypernova explosion can
vary.

Questions:
How many light years away was the 1604 explosion and roughly where was
it in our galaxy relative to the sun?

What was the estimated rough size (diameter) of its impact zone?

Brian Tung:
That would depend somewhat on whether it was a Type I or Type II
supernova. Type I supernovae, which result from a white dwarf exceeding
the Chandrasekhar limit of 1.4 solar masses (this may vary slightly
depending on composition), are more energetic than Type II supernovae,
which result from the collapse of a massive star. A Type II supernova
would be deadly to human life out to a distance of perhaps 10 to 20
light-years; a Type I supernova maybe a factor of two or three further.
I don't think these distances are known to great precision.

The December 27, 2004, outburst from the magnetic neutron star SGR
1806-20, _50,000 LY distant_, had an impact zone that included the
Earth. Radiation that it spewed forth compressed the Earth's ionosphere
for a short period, disrupting long-range HF radio communications.

"Whoppingly bright," said Dr. Brian Gaensler, an astronomer at the
Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "It
gave off more energy in 0.2 seconds than the Sun does in 100,000 to
200,000 years." (Quoted by the NYT.) It outshone the all the rest of
the stars in the Milky Way at certain wavelengths.

SGR 1806-20 is believed to contain about 1.5 solar masses in a sphere
about 20 KM in diameter; it rotates every 7.5 seconds, a leisurely rate
for a neutron star. Amazingly, following the outburst SGR 1806-20
remained intact, still rotating at the same rate.

Aaaah, the power of gravity!

Davoud