International Geophysical Year (IGY), international project of concentrated, coordinated exploration of Earth and its cosmic environment. The period chosen (July 1957-December 1958) was one of intense solar activity. During the project observations and experiments were conducted at more than 4,000 stations ranging from drifting ice-pack stations in the Arctic Basin to the South Pole in Antarctica and from trenches deep in the Pacific to satellites thousands of miles from Earth. Important results were obtained in many areas of geophysics.

Highlights included the launching of artificial satellites, which led to the discovery of the Van Allen belts surrounding Earth (see Radiation Belts), and soundings of the ocean floor, which contributed to the theory of plate tectonics. The IGY also resulted in the Antarctic Treaty, which in 1959 dedicated that continent to peaceful scientific investigation. A total of 66 nations took part in the IGY, which was coordinated by the International Council of Scientific Unions.