Parabolic radio telescope

The parabolic radio telescope was not invented—it crystallized. By 1937, every component needed was already scattered across laboratories and scrapyards: parabolic reflectors from optics, radio receivers from telecommunications, and antenna theory from physics. The only missing ingredient was a question worth asking.

Heinrich Hertz had demonstrated the principle in 1888, building a 2-meter zinc parabolic dish to prove Maxwell's electromagnetic theory. But Hertz was demonstrating propagation, not listening. The idea that the cosmos might be shouting at radio frequencies never occurred to anyone—until Karl Jansky was assigned to hunt static.

In 1933, Jansky rotated a bus-length antenna across a New Jersey potato field investigating interference plaguing transatlantic phone calls. He found a signal repeating every 23 hours and 56 minutes—a sidereal day. His friend Albert Skellett recognized it: the signal came from the Milky Way's center. The New York Times ran it on the front page. Astronomers, trained in optics and unfamiliar with electronics, ignored it. Bell Labs reassigned Jansky.

But radio engineer Grote Reber had read Jansky's papers. In summer 1937, working weekends in his Wheaton, Illinois backyard, Reber built the first purpose-built parabolic radio telescope: a 9.4-meter dish made from sheet metal, wood framing, and $1,300 of his own money. For nearly a decade, Reber was the world's only radio astronomer.

Then World War II arrived, and with it, stockpiles of microwave components and trained engineers. By 1957, the Lovell Telescope stood complete at Jodrell Bank—76.2 meters using gun turret gears from dismantled battleships. The cascade accelerated: Arecibo's 305-meter dish (1963), pulsars (1967), the cosmic microwave background (1964). The adjacent possible had opened.