Tuesday, March 20

a congeries of innumerable stars

Every culture has had an explanation for the Milky Way, that band of milky light that circles the sky from Orion to Sagittarius and back again, arching high on summer and winter evenings, hanging low near the horizon in spring and fall. A bridge. A river. The pathway of the spirits of the dead. A circular cord of downy feathers. A track of cornmeal. In the National Gallery in Washington, D.C., is a painting by Tintoretto, titled The Origin of the Milky Way, that depicts the Greek view of things: Milk spurts into the sky from the breasts of the goddess Juno as she tries to nurse the lively infant Hercules.

Galileo's telescope put such fabulous stories to rest. In his little book The Starry Messenger, he reported his observations: "For the galaxy is nothing else than a congeries of innumerable stars distributed in clusters. To whatever region of it you direct your spyglass, an immense number of stars immediately offer themselves to view." Not milk—nor feathers, nor cornmeal—but "congeries of innumerable stars." The evidence, as Galileo said, was indisputable. But astronomers for the next few centuries had other things on their minds besides those swarms of faint stars. Sun, Moon, planets, comets: their interests lay closer to home. Not until William Herschel turned his big new telescopes toward the stars in the late 1700s did the Milky Way again become an object of astronomical interest. Herschel plotted the positions of thousands of faint stars in three dimensions . . . We live in a disk-shaped cloud of stars, he concluded—a "grindstone," he called it—and he guessed that some of the other "fuzzy spots" in the sky were other Milky Ways of stars. We now know that he got it mostly right.

-- Chet Raymo An Intimate Look at the Night Sky