Hale's 200-inch telescope was a success in part because it observed at visible wavelengths. Compared to radio waves, visible light is very short. A radio dish of comparable power as Hale's telescope would be about a million times larger, spanning nearly a quarter of the United States.

Interferometry, though, liberated radio astronomers from the constraints of dish size. It was developed after World War II by astronomers at Cambridge and creates a single virtual telescope out of several individual dishes spread about. [Interferometry 101]

The Very Large Array, in Socorro, New Mexico, is one of the most powerful interferometers. The first of the 27 antennas was erected in 1975. Each antenna in the Y-shaped array is 82 feet (25 meters) wide and weighs about 230 tons. Before its formal dedication ceremony in 1980, the VLA was already providing useful data to the scientific community.

"Suddenly, radio astronomy went from being a science that could only get crude images to being able to get the best images of all," Tucker says.

The dishes, which are on tracks and can span up to 22 miles, together have a power comparable to seeing a golf ball -- emitting radio signals -- 100 miles away. Astronomers have used the VLA to detect water on Mercury, to image the first gravitational lens, and to map and study cosmic jets.

The array is also used to examine black holes, from the mouths of which come radiation in many forms, from radio to X-rays.