A certain age-old nosiness lies at the origins of modern astronomy. For centuries scientists and philosophers dreamed of a fabulous device which would abolish distance. The heavens, which ancient star-gazers searched as much for signs and portents as for clues to their mysterious operations, would then disclose their secrets to our peering eyes.

But a stronger impetus than the quest for scientific knowledge often fed these longings; in many cases, the military advantages alone promised to be decisive. According to legend, Julius Caesar possessed the secret of a magical “glass” that he used to spy on enemy troop movements across the English Channel. The invention of some sort of “far-seeing” instrument — the literal meaning of the word “telescope” — was prompted as much by the possibility of improved espionage as by sheer scientific curiosity. It’s no coincidence that the telescope was once called a “spyglass.”

The first recognizably modern telescope was invented in The Hague and appeared on the market in 1608. By modern standards it was a crude instrument with a magnification of only three times, but in its design it represented an immense advance. Within a year, however, Galileo Galilei (1564–1642) had copied the design, improving its power of magnification first to eight, and then, a mere three months later, to 20. Previously, Galileo had used a combination of a lens with a mirror in his studies of the heavens, but the Dutch instrument was a refractory telescope, employing a convex glass objective with a concave glass eyepiece, and it offered superior resolution. It was with this improved telescope that he was able not only to observe the lunar surface in unprecedented detail but to discover four of the moons of Jupiter. He reported these discoveries in his “Starry Messenger.” That epochal book, which Galileo rushed into print, appeared on March 13, 1609, almost four centuries ago this week.

This story seems straightforward enough, but in her fascinating new study “Galileo’s Glassworks: The Telescope and the Mirror” (Harvard University Press, 231 pages, $21.95), Eileen Reeves shows just how tangled with myth and legend the history of the telescope, and Galileo’s pioneering use of it, actually was. Ms. Reeves has set out to illustrate “the role of misinterpretation, error, and preconception” in scientific discovery. To this end she traces the various fanciful accounts of ancient and medieval telescopic devices — from “burning mirrors” to the great lighthouse, or pharos, of Alexandria — most of which served strategic rather than scientific aims. A swarm of learned but quite shadowy figures, from outright charlatans and scoundrels to men of genius, enlivens her account.

In one of her most suggestive illustrations, she reproduces a Turkish miniature from around 1582 that shows two turbaned observers gazing raptly on the glowing dome of the Alexandrian lighthouse. Legend had it that the lighthouse, fitted with an immense mirror, provided a panoramic and telescopic vista of the harbor for defensive purposes. But the lighthouse also represented an immemorial ambition. In 1267, 30 years before, the English natural philosopher Roger Bacon had written of “the wonders of refracted vision.” And a century later, students at Oxford were reportedly still being distracted by Bacon’s marvelous “mirror,” which showed “what people were doing in any part of the world.” The report is fanciful, but it shows that what we now regard as commonplace — television, along with the telescope — were once barely imaginable wonders.

Ms. Reeves guides the reader through what sometimes resembles a dusty museum of discarded instruments. “Imperial” mirrors, conceived to incinerate enemy fleets, “shadow squares” for use in altimetry, alongside such curiosities as “Lesensteine” or “reading stones,” crude magnifiers made of mineral, as well as clunky medieval reading glasses — first attested around the year 1280 — bear witness to our perennial yearning not only to see ever farther and ever more sharply but to turn that farsightedness to advantage. Galileo himself exemplified this doubleness of motive. At the same time he was observing the skies more precisely than anyone before him, he was also offering his improved telescope to the Doge of Venice for military use, in the hope of gaining a permanent position.

Ms. Reeves recounts this complicated history with great flair. She is more interested in the missteps and the stumbles that accompanied momentous discoveries than in their scientific significance, and rightly so. The tale of Galileo’s telescope is, as it turns out, an intensely human one. Sometimes, amid the intrigue and the campaigns of slander and distortion which surrounded Galileo’s discoveries, it seems as if the chief obstacle to a clear-sighted gaze at the heavens lay not in better optics but in piercing dense clouds of misconception. As Ms. Reeves shows, Galileo was no isolated genius; he built on the scattered findings of his predecessors. To certain contemporaries, he appeared as a modern Prometheus, but he was also a shrewd operator, as ambitious as he was inquisitive. There was something both sublime and stubborn in his nosiness, yet in the end it led him to the stars.

eormsby@nysun.com