Telescopes from the Ground Up

A giant telescope relies on multiple dishes

Because radio waves are so large — about 100,000 times longer than visible light waves — astronomers need colossal telescopes to collect them.

Building a single telescope large enough is impossible, so radio astronomers build arrays. Arrays are huge series of telescopes that work together as one telescope. The Very Large Array, or VLA, is such a telescope with the same resolving power as a single telescope 22 miles (36 kilometers) in diameter. One dish this size would cover more area than New York City, with all its buroughs.

Radio telescopes have come a long way since Grote Reber built the first one in his backyard. Astronomers have built larger and larger radio telescopes that can track radio sources across the sky. In addition, they learned how to link single dishes together and make them work like a single telescope, called an interferometer. Interferometers are used to increase the resolving power of a telescope.

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Radio Telescopes
Map of Socorro, New Mexico, USA, where the Very Large Array is located.
Two image: one an aerial view of one of the configurations of the VLA and another a closeup of one of the individual radio telescopes.Enlarge picture
The Very Large Array (VLA)
Year completed: 1980
Telescope type: Reflectors
Light collector: 27 metal reflectors
Mirror diameter: Each 82 feet
(25 m)
Light observed: Radio
Discovery Highlights:
  • With its ability to see fine detail, the VLA detected that Mercury has water ice on the floors of craters at its north pole.