On the grandest of scales, the universe is like a spider web. Strands of galaxies can stretch across a billion light-years or more, separated by wide spaces known as cosmic voids. The first big strand in the web was reported 25 years ago today. Known as the Great Wall, it’s hundreds of millions of light-years long and contains tens of thousands of galaxies. The wall was discovered by Margaret Geller and colleagues at the Harvard-Smithsonian Center for Astrophysics. They were producing three-dimensional maps of how galaxies are distributed — not just where they appear in the sky, but how far away they are as well. Their first plots revealed a shape that resembled the stick figure of a man, with a thick body and spindly arms and legs. The “body” was the Great Wall — a dense ribbon of clusters and super clusters of galaxies that’s a few hundred million light-years away. Before the Great Wall, it was generally thought that galaxy clusters were pretty evenly spread. But the Great Wall and s
