And the largest cosmic ray observatory, Pierre Auger Observatory in Argentina clocks in at around 3000 km^2. https://en.wikipedia.org/wiki/Pierre_Auger_Observat

And the largest cosmic ray observatory, Pierre Auger Observatory in Argentina clocks in at around 3000 km^2. https://en.wikipedia.org/wiki/Pierre_Auger_Observatory https://en.wikipedia.org/wiki/Pierre_Auger_Observatory A very different and really neat concept that hasn't become real yet is JEM EUSO, a telescope that would be mounted on a space station, pointed at Earth, would detect air showers via fluorescence like Auger's fluorescence telescopes do on the ground. This could theoretically cover a much larger area than traditional CR observatories. https://en.wikipedia.org/wiki/JEM-EUSO https://en.wikipedia.org/wiki/JEM-EUSO