On a warm July day in 1972, NASA launched a new Earth-imaging satellite called the Earth Resources Technology Satellite. "ERTS" was the first satellite of what later became NASA and the U.S. Geological Survey's Landsat Program, an ambitious effort with a vision of documenting the entirety of Earth from space. The first Landsat was so successful it led to a series of satellites that have created the longest contiguous record of Earth's surface from a space-eye view—that continues growing to this day, 50 years later.