Why do we call this system a “telescope,” and what will make it as big as any possible Earth-based telescope? Galileo was the first experimenter to use telescopes to look at the heavens. Of course the telescopes that he used, and most of the ones used by astronomers and amateurs since that time, allow observation of the heavens by the visible light emitted by stars.
Visible light is only one way to observe, though, and many other kinds of radiation have been used to observe the skies. Observations have been made using radio waves, microwaves, gamma rays, infrared light, ultraviolet light, and even neutrinos, x-rays, and gravitational waves emitted and reflected by astronomical objects. Scientists have built very elaborate systems to detect cosmic rays, too.
All of these observational systems are called telescopes because each of them allows scientists (and amateurs) to “see far” in different ways. “Seeing far” is what any telescope does, no matter what kind of radiation it is sensitive to. So, it is fair to call the entire ERGO Energetic Ray Global Observatory a “telescope.” ERGO will be formed by sensitive detectors placed in classrooms all over the planet. When all the data is assembled and coordinated, a kind of real-time image of the cosmic-ray sky will result. As Earth revolves and orbits the sun, the telescope will scan every direction in the sky. Such an imaging system has never been created on such a large scale.