William Herschel, the discoverer of Uranus, was the first to explore the region beyond the rainbow of visible light. In 1800, he reported on experiments to determine the heating power of different colors, in which he let a spectrum of light fall on a set of thermometers. To his surprise, he found that the greatest heat was produced off the red end of the spectrum where nothing was visible. Herschel had discovered infrared radiation. In the mid-19th century, astrophotographers began to explore the other end of the spectrum.
Photographic emulsions are particularly sensitive to shorter wavelengths of light, blue and violet.
Physicists completed the picture in the late 19th and early 20th centuries with the discovery of radio waves, ultraviolet light, x rays, and gamma rays. Astronomers came to realize that many astronomical bodies radiate little or no visible light at all and remain hidden without full spectral exploration. Trying to understand the universe through visible light alone is like listening to a Beethoven symphony and hearing only the cellos. Only by studying images and spectra taken across the entire electromagnetic spectrum can astronomers appreciate the full scope of the universe. In the 1930s, Karl Jansky, an engineer for Bell Labs, took the first step in opening up the entire electromagnetic spectrum when he discovered radio waves from deep space using a simple antenna.