> Which of the following would be brighter, in terms of the amount
> of energy delivered to your retina:
> * A supernova, seen from as far away as the Sun is from the Earth, or
> * The detonation of a hydrogen bomb pressed against your eyeball?
>
> ... the supernova is brighter ... by nine orders of magnitude.
We're all made from star dust, and will become star dust again.
They're actually much closer to equal, if you account for the duration of the supernova light curve.
It's a somewhat relevant difference. A supernova 4 light years away, with all the energy released instantaneously like a bomb, should ignite and vaporize everything on one-half of the planet. That's a wrong calculation. The peak rate— the peak luminosity of a type Ia supernova, for example (10^43 erg/s or 10^36 W—a famous standard candle) would be no more than 50 W/m^2, from the distance of Alpha Centauri. That's about a 5% addition to the solar irradiance, sustained over a few weeks—probably just a moderate change in weather patterns.
GP and XKCD are talking about a supernova from the Sun, you're talking Alpha Centauri.
(That's the less important part of my comment, and I'm not sure why people latched onto it! The important part is that supernovae are >7 orders of magnitude slower than hydrogen bomb explosions).