...ever to be visible to unaided human eyes. For a few seconds it reached a visible magnitude of 5.8, which is about the dimest star you can see in a dark sky.


A bit more about it from Bad Astronomy Blog

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Yesterday, a gamma-ray burst went off that was so bright that had you been looking at the right spot in the sky you could have seen it with just your own eyes!

Artist Dana Berry's drawing of a gamma ray burst going off. It’s difficult to put this into the proper context. GRBs are monumental explosions, the exploding of a massive star where most of the energy of the catastrophe is channeled into twin beams of energy. These beams scream out from the explosion like cosmic blowtorches, and for thousands of light years anything they touch is destroyed. Happily for us, GRBs always appear hundreds of millions or billions of light years away.

Let me put this in perspective for you. Imagine a one megaton nuclear weapon detonating. That’s roughly 50 times the explosive yield of the bomb dropped on Nagasaki. Devastating.

The Sun, every second of every day of every year, gives off 100 billion times this much energy. That’s every second. A star is a terrifying object.

In the few seconds that a gamma-ray burst lasts, it packs a million million million times that much energy into its beams. In other words, for those few ticks of a clock the GRB is sending out more energy than the Sun will in its entire lifetime.

There is, quite simply, no way to exaggerate the devastation of a gamma-ray burst.

Yet for all that, they are optically faint due to their terrible distance. At billions of light years away, even the Universe’s second biggest bangs are difficult to see.

So that’s what makes GRB 080319B (the second GRB seen on 2008 March 19) so incredible: distance measurements put it at 7.5 billion light years away, yet it was visible to the unaided eye had you just happened to be looking up at the sky at that moment.

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