Who used globular clusters to show the Sun is far from the Milky Way's center?

Harlow Shapley used globular clusters to show that the Sun is far from the Milky Way’s center. In the 1910s and 1920s, he estimated distances to globular clusters and mapped their distribution across the sky.

Globular clusters are dense, ancient groups of stars that orbit mainly in the Galaxy’s halo. Shapley noticed that they were not distributed evenly around the Sun: their concentration pointed toward the constellation Sagittarius, indicating that the Galactic Center lay in that direction rather than near Earth. His work helped overturn the older idea that the Sun occupied a central position.

Shapley correctly established the Sun’s off-center location, although his distance estimates were too large. Interstellar dust dimmed many distant clusters, making them appear farther away than they really were. Modern measurements place the Sun roughly 26,000–28,000 light-years from the Galactic Center. A related historical confusion is that Shapley’s result addressed the Milky Way’s structure, not the later question of whether spiral nebulae were separate galaxies.