Telescopes

When you start stargazing with a telescope, two experiences typically ensue. First, you are astonished by the view—Saturn’s golden rings, star clusters glittering like jewelry on black velvet, galaxies aglow with gentle starlight older than the human species—and by the realization that we and our world are part of this gigantic system. Second, you soon want a bigger telescope.

Galileo, who first trained a telescope on the night sky 400 years ago this fall, pioneered this two-step program. First, he marveled at what he could see. Galileo's telescope revealed so many previously invisible stars that when he tried to map all of them in just one constellation, Orion, he gave up, confessing that he was "overwhelmed by the vast quantity of stars." He saw mountains on the moon—in contradiction to the prevailing orthodoxy, which declared that all celestial objects were made of an unearthly "ether." He charted four bright satellites as they bustled around Jupiter like planets in a miniature solar system, something that critics of the Copernican sun-centered cosmology had dismissed as physically impossible. Evidently the Earth was a small part of a big universe, not a big part of a small one.