When Marconi sent his radio waves from Poldhu to America, he was helped by something that he didn’t know existed: the Earth’s ionosphere, a layer of charged particles high in the atmosphere that can reflect electromagnetic waves back toward the surface of the Earth.  Since the density and location of the charged particles in the ionosphere is highly variable, today we use a more-reliable system to gather in our radio waves and send them over the horizon: telecommunications satellites.  The ground installations of transmitters and receivers that utilize these satellites are called “earth stations,” and we’ll end the electromagnetic telecommunication portion of our course at the largest satellite earth station in the world: Goonhilly.