Humans can only see visible light—the portion of the electromagnetic spectrum that is visible to the human eye. That's why so hard to study celestial objects hidden behind cosmic dust. But radio astronomy reveals those parts of the Universe that can't be seen in visible light—and the secrets of dust-shrouded galaxies like our lovely Milky Way.
Objects both on Earth and in space emit other types of detectable electromagnetic radiation, such as radio waves, which penetrate dust. And our beautiful, giant radio telescopes can see those phenomena based on the radio waves they emit. They observe the longest wavelengths of light—ranging from one millimeter to over 10 meters long—and through their sophisticated eyes, we are able to watch stars and planets be born and die, study galaxies and black holes, see the echo of the Big Bang and the Universe’s first galaxies. With arrays of big enough radio telescopes, in the near future astronomers are going to create a much sharper and more detailed map of invisible dark matter—which is estimated to constitute as much as 85 percent of the total matter in the universe.