How many 25-meter radio telescopes make up the array?

• A. Sixteen 50 m telescopes
• B. Twenty-eight 25 m radio telescopes
• C. Thirty-two 20 m telescopes
• D. Forty 15 m telescopes

Answer: (B)

In a radio telescope array, the number of individual dishes determines how many separate collecting elements the array has, and it’s those elements that form the baselines used to synthesize high-resolution images. If the array is described as consisting of 25-meter dishes, the total number of those dishes tells you how many elements you’re combining. Here, the configuration is 28 dishes, each 25 meters across. That means you have 28 independent elements contributing to the interferometric measurements, which yields a large number of baselines and therefore strong resolving power. The total collecting area also scales with the number of dishes, so more dishes increase sensitivity as well. The other options mix different dish sizes or counts, which wouldn’t match the description of an array built from 25-meter telescopes. So the correct match is 28 telescopes of 25 meters each.