The first person to detect radio waves coming from space was Karl Guthe Jansky, an American physicist and radio engineer. In the 1930s, Jansky was working for Bell Telephone Laboratories and was investigating the source of static interference that affected long-distance telephone communications. In 1931, he built a large directional antenna system that could be rotated to different positions, and he used it to study the static interference.
During his experiments, Jansky discovered that some of the static interference originated from the Milky Way galaxy. He identified three types of static: a steady hiss, a stronger and less frequent static, and a third type of static that had a regular pattern, corresponding to the rotation of the Earth. The third type of static led Jansky to conclude that it was coming from outside the Earth's atmosphere.
Jansky's discovery of radio waves from space marked the birth of the field of radio astronomy. His work laid the foundation for further research in the field, which has since led to significant advancements in our understanding of the universe using radio telescopes.