In the early 1930s, a young engineer named Karl Jansky was given a puzzling job. His employer, Bell Telephone Laboratories, wanted him to figure out what was causing static on long-distance phone calls. Jansky built a large antenna that could rotate in a full circle. He set it up in a field in New Jersey. By May 1933, Jansky had found three sources of the static. Two were nearby thunderstorms. The third was something mysterious. It was a steady hiss that came from the same direction in the sky every day. After months of careful tracking, Jansky realized the signal was coming from the center of the Milky Way -- our own galaxy. The stars and gas clouds at the galaxy's core were sending out invisible radio waves. These waves traveled across thousands of light-years to reach Jansky's antenna. Nobody had ever detected signals from deep space before. Jansky had accidentally discovered that the universe was broadcasting on a frequency humans could build machines to receive. His discovery created the field of radio astronomy. Today, giant radio telescopes around the world listen to signals from distant galaxies, exploding stars, and even the leftover glow of the Big Bang.