International Geophysical Year (IGY), a period of extensive study of the earth by geophysicists and other scientists of many countries working in close cooperation. The International Geophysical Year was held from July 1, 1957, to December 31, 1958. The 18-month year was scheduled to coincide with a peak period in the sun's energy cycle, which influences the earth's magnetic field and the ionosphere. IGY scientists from 66 nations, under the direction of the International Council of Scientific Unions, carried out experiments and observations in all parts of the world. Governments and universities supported the project, which cost about $500,000,000. The most spectacular achievement of the IGY was the launching of the first artificial satellites. Much IGY activity took place in Antarctica.