Harlow Shapley 
Our home galaxy, the Milky Way, is a giant “island universe” in a universe that’s filled with them. Harlow Shapley understood the first part of that description better than any astronomer before him. But he missed out on the second part -- he thought the universe ended at the edge of the Milky Way.
Shapley was born 125 years ago tomorrow in Nashville, Missouri. He began his career as a journalist, but soon turned to astronomy.
At Mount Wilson Observatory in California, he studied the big, dense balls of stars known as globular clusters. He mapped their positions in the sky, and noted that they seemed centered around a point in Sagittarius.
Shapley realized that this point was the center of the galaxy. He plotted its distance at about 50,000 light-years. That made the Milky Way far larger than anyone had thought. And even though Shapley’s numbers were off, he was still much closer to the galaxy’s true size than anyone else before him.
But Shapley was wrong about what that meant for the size of the universe. Like many others, Shapley thought the Milky Way was the sum total of the entire universe. Others thought that the Milky Way was but one galaxy of stars in an incredibly vast universe.
In 1920, Shapley debated another astronomer on the topic. Shapley’s viewpoint carried the day. Just a few years later, though, it was proved wrong. The Milky Way is but one of many giant “islands” of stars in the vastness of the universe.
Script by Damond Benningfield, Copyright 2010