CHICAGO, ILLINOIS—When Galileo Galilei shook up the scientific community with evidence of a heliocentric world, he had a little tube fitted with two pieces of glass to thank. But just how this gadget evolved in the nascent days of astronomy is poorly known. That uncertainty has inspired a group of researchers to compile the most extensive database of early refracting telescopes to date , presented here yesterday during a poster session at the annual meeting of AAAS, which publishes Science. Now, the scientists plan to use modern optics to recreate what Galileo—and the naysaying observers of his time—experienced when they first peered through these tubes at the rings of Saturn, the moons of Jupiter, and the phases of Venus.
The database, called Dioptrice, went online earlier this month. It contains records of about 1300 telescopes—mostly physical artifacts from museums and private collections, but also descriptions in books and depictions in art—that date from 1610 to 1775. Those years marked a formative period for the telescope, explains Stephen Case, a science historian and graduate student at the University of Notre Dame in Indiana who helped compile Dioptrice. For the last 2 and a half years, he has pored over books in attic of Chicago’s Adler Planetarium and tracked down telescopes in museum catalogs from galleries around the world.
The first phase of the project involved documenting the origin and design of each telescope. Case and his colleagues concluded that most were used for military purposes, such as spotting distant ships or approaching troops, or were simply collected as status symbols, before they achieved widespread scientific use.
But phase two will look deeper at the optical abilities of the telescopes. Their designers weren’t yet able to make perfectly curved class, so the lenses had jagged edges and a small field of view. And until the mass production of the achromatic lens around 1775, they couldn’t correct for the fact that different wavelength of light refract at different angles and cause a blurry image at the focal point. Yet the crude setup inspired a string of eureka moments. “Galileo suddenly could see the phases of Venus,” Case says. “He could see the moons orbiting around Jupiter. He suddenly had evidence for the heliocentric cosmology.”
To precisely test how these devices transmitted distant light, the group will use adaptive optics—the technology behind today’s large telescopes. These rely on a grid of deformable mirrors that tilt to adjust for the light-bending turbulence of the atmosphere. The researchers will essentially run that process in reverse, Case says, feeding a light source with a grid structure into the telescope and observing how that grid gets distorted when passing through 400-year-old glass. If the light source is an image of Saturn or Jupiter, Case explains, you can “get out on the other end what that telescope would have shown you.”
Such tests could reveal whether a given telescope could conceivably show a separation between the rings of Saturn, for example. But Case points out that what a scientist perceived in these instruments also depended on his trained eye and his sense of what to look for. In other words, no adaptive optics system can account for a given stargazer’s interpretation, or apply the Galileo filter.
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