How did Harlow Shapely determine where the center of the galaxy lies?

Harlow Shapley determined the center of the Milky Way galaxy by studying the distribution of globular clusters, which are dense groups of stars orbiting the galaxy. He mapped their positions and distances, finding that they were concentrated in a specific region of the sky, which he identified as the galactic center. By analyzing the clusters' distances using variable stars known as Cepheid variables, Shapley concluded that the center of the galaxy is located in the direction of the Sagittarius constellation, specifically around the area of the supermassive black hole known as Sagittarius A*.