Venturing into space truly altered our understanding of our home. When humans moved out of low Earth orbit for the first time in 1968, we saw our home planet suspended and alone in space-with no national borders visible to the wider universe. That sight, shared with the world in a photograph, helped spark the modern environmental movement. One astronaut commented that we'd gone forth to explore outer space but ended up discovering the Earth. The first Earth Day was celebrated less than two years later. And in the decades since, as we began to explore the solar system, Earth remained the ultimate focus of all space exploration. The planetary probes that study alien environments give us valuable data about how our own planet developed and works. Our constellations of Earth-orbiting satellites support the global communications and positioning grids that have changed our lives. And of course, Earth observation has revolutionized our understanding of the greatest threat to life on Earth today-anthropogenic climate change.
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