When the first artificial satellites were sent into orbit around the earth in 1957, some way of tracking them was called for. As early as 1955, the Smithsonian Astrophysical Observatory (SAO), as part of its contribution to the International Geophysical Year of 1957-1958, had organized project Moonwatch, a program coordinating amateur astronomers around the world into teams for visual satellite tracking. Reports of Moonwatch volunteers’ observations of the early Sputnik, Explorer, and Vanguard satellites were sent to SAO and processed by scientists, who then determined the satellites’ orbits and also derived information about the Earth’s upper atmospheric density. Moonwatch continued to operate into the 1960s. Pictured here is a Japanese team of Moonwatch observers at their stations.