This story appears in the October 2020 issue of National Geographic magazine.
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The map that NASA launched in 1972 could lead extraterrestrials to Earth. A new map, nearly 50 years later, provides even better directions.
A sparkling mass containing at least half a million stars—and some two dozen pulsars—the globular cluster known as 47 Tucanae is one of roughly 150 ancient stellar clumps orbiting the Milky Way galaxy.