Radio Astronomy: Observing the Invisible Universe

Take a tour of our neighboring planets via their radio emissions and learn how scientists infer their temperatures and energy sources. You'll be shocked by the difference between their images in reflected sunlight - the images we're familiar with - and their appearance when we "see" the radio energy they emit on their own.

When young engineer Karl Jansky was tasked to find natural radio sources that could interfere with commercial transatlantic radio communications, radio astronomy was born. His work led to the discovery of synchrotron radiation. But it would be decades before scientists understood what these earliest radio astronomers had detected - cosmic rays and magnetic fields.

Not long after the birth of radio astronomy, a Dutch student used what was then known about the physics of atoms to determine that if hydrogen existed in interstellar space, it would produce a specific spectral line at radio wavelengths. In 1951, the line was detected at 21 cm, exactly as predicted. At that moment, our understanding of the universe forever changed.

Radio telescopes are so large because radio waves contain such a small amount of energy. For example, the signal from a standard cell phone measured one kilometer away is five million billion times stronger than the radio signals received from a bright quasar. Learn how each of these fascinating instruments is designed to meet a specific scientific goal.

Before there were stars and planets, before there were galaxies, there was hydrogen - and we still have more hydrogen today than any other element. Understanding the quantum physics of this simplest atomic structure, and using the Doppler shift and models of differential rotation in the Milky Way, astronomers have made myriad astounding discoveries about the universe. It all starts with hydrogen.