As the name would suggest, radio astronomy is the study of celestial objects by the radio waves they emit. Radio astronomy began, in a way, with the Guglielmo Marconi's first radio transmission in 1901. Amateurs were given the short wavelengths to listen to (termed shortwave radio), and the first transatlantic reception occurred in 1921.

Shortwave communication aroused great interest by telephone companies, and engineers from AT&T studied the static that such communications produced. This static was later identified as coming from other parts of the galaxy. In the 1930s Grote Reber built one of the first satellite dish antennas, about 32 feet in diameter, and larger ones continue to be built today.

FIGURE 16-3: The dome covering a radio telescope at Kitt Peak, near Tucson

One problem with radio astronomy is interference. Some signals from the cosmos are so weak that even when astronomers—with the best equipment—are listening on certain frequencies, radio stations transmitting on nearby frequencies can cause interference. Static can even be caused by poorly designed devices we use every day, such as garage-door openers and cellular telephones, as well as by transmitters that orbit Earth in satellites.

The National Radio Astronomy Observatory is part of the National Science Foundation, and builds radio telescopes for use all around the world. Radio telescopes are ideal for studying pulsars, quasars, and hypothesizing about radiation from the Big Bang. In fact, they are virtually the only way to study these types of subjects, and in this respect radio astronomy has revolutionized our ability to gain knowledge about the cosmos.

The Very Large Array (VLA) in New Mexico, consists of 28 separate dish antennas. The VLA was constructed between 1973 and 1981. Each dish has a diameter of 81 feet, with a combined antenna amounting to 422 feet in diameter. The dishes are laid out in a Y-pattern spread over an area that is larger than Washington, D.C. The telescopes can be moved into different configurations, depending on their observing target.

FIGURE 16-4: Arecibo radio telescope