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Predictions of Doom

An example of things I think about while walking to work:

The earth is about 1.5e-5 light years from the Sun; there are plenty of stars massive enough to end their lives in a supernova within 100 light years of the solar system. 100 light years is about 6.5 million times further from the earth than the Sun. Luminosity follows an inverse square law, so a Sun-like object 100 light years away is about 42e12 times less luminous than the Sun.

However, a supernova is massively intense, something like 5 billion times brighter than the Sun. So we can expect a supernova at that distance to appear about .01% as bright as the Sun. This is about 10 magnitudes dimmer, because 5 magnitudes is a factor of 100 and magnitude is a logarithmic scale.

The Sun has an apparent magnitude of about -27, so our hypothetical supernova would appear at about magnitude -17. This is still about 100 times brighter than the full moon (mag -12), so a supernova that close would be a HUGE appearance in the night sky, possibly making it seem like dim daylight. I wonder if that would have any effects on the circadian rhythms of some biological species, and how that might affect life on earth.

My math may be all wrong; I was doing it all in my head. I am still curious, though. At first I got answers implying that such a close supernova would outshine the sun, but I had forgotten about the inverse square law, which makes all the difference.



( 2 comments — Comment )
May. 10th, 2007 06:18 pm (UTC)
Heh. And then there's the "Gamma ray burst" which is hypothesized to be the sort of thing which wipes out all life on a planet.
May. 11th, 2007 06:28 am (UTC)
After I posted that I was doing some random research and found several references to Eta Carinae, which is 7500 light years away but so massive that it's expected to form a "hypernova" nearly a trillion times brighter than the Sun. Even at that distance, there's apparently considerable worry about the intensity of the energy burst as received here on earth, particularly mutagenic X-rays and gamma rays, and the effect of the intense UV on certain sensitive species. Even conservatively, there would be significant effects on spacecraft and on the ozone layer.
( 2 comments — Comment )



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