Typically, the only cosmic things that disturb the "sunny side" of Earth's atmosphere come from our closest star, the Sun.
Except, it turns out, if you get a very bright GRB, the brightest we ever detected. And suddenly a star, exploding 2 billion light-years away (the Sun is just 8 light away!) can - just temporarily, for a few minutes, but still - affect the Earth's ionosphere (and possibly the ozone layer).
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