That array could be “either a radio interferometer on the farside surface of the moon or a slowly drifting constellation of many small satellites.”

When two telescopes in a radio interferometer make a common detection—when both telescopes record the same exact light waves—astronomers say they “found fringes” between the two sites.

Why has it taken so long to put a low-frequency radio interferometer on the moon?

They used a radio interferometer, which measures radio waves and shows which direction they come from, and studied the radio pulses generated at the onset of lightning.