It's huge. Normally, the curvature of the earth would make it impossible to detect anything at such distances. But the ionosphere's lower levels act like a waveguide [1], (and this tells you which frequencies you should listen on to take advantage of this).
The craziest phenomenon of this kind is whistlers [2]. Lightning strikes can be heard on radio at a point on the earth exactly symmetrical to the source, using the equator as plane of symmetry. In fact, the signal bounces around back and forth between the two points, following a line on the magnetosphere. The ones closer to the poles have longer paths, and their frequencies can get spread out over 3-4 seconds as they bounce around.
Cool stuff. I'm partial to the theory that prior mass extinctions have involved a meteor strike causing a whistler like effect on the opposite side of the plane causing volcanic action. eg https://en.wikipedia.org/wiki/Large_igneous_province#Meteori...
The craziest phenomenon of this kind is whistlers [2]. Lightning strikes can be heard on radio at a point on the earth exactly symmetrical to the source, using the equator as plane of symmetry. In fact, the signal bounces around back and forth between the two points, following a line on the magnetosphere. The ones closer to the poles have longer paths, and their frequencies can get spread out over 3-4 seconds as they bounce around.
[1]: http://en.wikipedia.org/wiki/Earth%E2%80%93ionosphere_wavegu...
[2]: http://en.wikipedia.org/wiki/Whistler_%28radio%29