How Do Astronomers Use Radio Waves?

Radio Astronomy

• Astronomers were limited to using optical telescopes to explore the universe for much of history, including the first part of the 20th century. That changed with physicist Karl Jansky's discovery in 1933 that certain types of astronomical objects emit radio noise. His discoveries led to the development of radio astronomy and took the science of astronomy beyond the visible to the invisible, advancing the understanding of the universe.

Radio Telescope

• Astronomers receive radio waves through a radio telescope. The radio telescope consists of an antenna -- typically in the shape of a dish -- and a receiver both pointed toward space. Because radio wavelengths are so much longer than visible ones, radio telescopes must be far larger than their optical counterparts to be as effective. For example, the dish of the Arecibo radio telescope in Arecibo, Puerto Rico, measures 1,000 feet across.

Radio Waves In Space

• Celestial objects emit radio waves for several different reasons, and the radio telescope can receive these radio waves and translate them into a format the astronomer can understand. Planets emit thermal radiation, which in turn creates a radio wave. Electrons in interstellar space produce radio-frequency noise, and atomic and molecular transitions in gases around stars result in radio wave emissions. Neutron stars also produce radio waves as their fast spin generates a strong magnetic field.

Discoveries

• The radio telescope was key in confirming the existence of neutron stars, or "pulsars," back in 1967. The fast spin of the remains of a collapsed star creates a rhythmic pulse of radio noise, confirming astronomers' prediction 30 years earlier of the existence of such stars. Other discoveries made possible by radio astronomy include black holes, evidence of the "Big Bang" itself, and the existence of hydrogen and carbon molecules in interstellar space.