By Thomas Hayden

Edwin Hubble trained as a lawyer–and became one of the most important astronomers of the 20th century. But the Rhodes scholar spent much of the 1920s doing something not much different from your average member of the paparazzi: snapping shot after shot after shot of elusive stars through the largest telephoto lens available. In Hubble's case, that "lens" was the 100-inch Hooker Telescope at the Mount Wilson Observatory in Pasadena, Calif., and he stalked distant nebulae, not Hollywood starlets. But just like the image-driven culture of celebrity, Hubble's legacy–the orbiting space telescope that bears his name and the revolutionary notion that we live in a vast and expanding universe–would have been impossible without photography.

It's not surprising that photography, an extension of human vision, has played a central role in the development of modern astronomy. The science began, after all, when humans first turned their inquiring eyes heavenward. Today, powerful observatories dot remote mountaintops and plateaus around the world, collecting light from the cosmos and capturing it on sensitive electronic detectors. Some 380 miles above, the Hubble Space Telescope orbits clear of the distorting influence of our atmosphere, its three cameras augmented by other light-measuring sensors. Farther out still, camera-bearing robotic probes have snapped intimate portraits of all our planetary siblings save Pluto and given us close-ups of nearby asteroids.

The first snapshot of a celestial object may have been taken by Daguerre himself, shortly before the public introduction of his imaging technique in 1839. (Most accounts credit British-born American chemist John Draper with taking the first daguerreotype of the moon in 1840. Neither image survives.) Photography soon became an essential part of astronomy, allowing observers to compare what they saw in the sky, night after starry night. As technology improved, long exposures revealed features too faint for eye and telescope alone. "Photography is not just a recorder of what can be seen," says astrophotographer David Malin of the Anglo-Australian Observatory in New South Wales. "It is a detector of what otherwise would go unseen." Early images aided in the discovery and characterization of comets, diverse star types, and the mysterious cloudlike nebulae, which Hubble would eventually show to be distant star clusters rather than pockets of gas in our own galaxy. And in 1930, photographic evidence finally proved the long-suspected existence of a ninth planet, Pluto.

Photography's full impact wasn't felt until the technology matured in the second decade of the 1900s. The development of dry emulsions meant that researchers like Vesto Slipher of Arizona's Lowell Observatory could expose a single plate for several nights running. That painstaking technique allowed Slipher to record the faint bands of color produced when he split incoming light into its constituent wavelengths with a prism. Using these spectra, he discovered that spiral nebulae spin rapidly and measured their speed. Building on Slipher's work, Hubble showed that the remote points of light were in fact distant galaxies, and that the universe was a far larger thing than anyone had thus far imagined. Even more important, he proved that the galaxies were moving away from us, and from each other. "Without photography, it would not have been possible to discover the expansion of the universe," says Kenneth Lanzetta, an astronomer at the State University of New York-Stony Brook. "It was a truly spectacular, worldview-changing aspect of astronomy."

The work of Slipher, Hubble, and others helped support Einstein's general theory of relativity and formed the basis for the big-bang theory. Hubble in particular sketched out the "master narrative" of modern astronomy, says David DeVorkin, a curator at the National Air and Space Museum, whose upcoming exhibit "Explore the Universe" includes the camera Hubble used to discover the expanding universe. Traditional photography may have been eclipsed by more exotic techniques, notes DeVorkin, but the revolutionary concepts it introduced still shape the study of the cosmos. "We've been working with those ideas ever since," he says, "filling in the spaces."