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xkcd #2878: Supernova
(imgs.xkcd.com)
Alt text:
They're a little cagey about exactly where the crossover point lies relative to the likelihood of devastating effects on the planet.
At some distance, we can no longer see the stars or even the galaxy. A supernova will allow us to see in really distant past, maybe at the first generation with some really good lensing.
Think ereandel but older