The Early Days

Astronomy may not be the oldest profession, but humans have been staring into the heavens since at least the dawn of civilization. Some of the earliest written records, from ancient Sumer, describe the patterns of the constellations, the locations of bright stars, and the motions of planets, beginning a 6000-year written record of astronomical investigation.

For almost all of that time, the only tools available to observers were their own eyes and a few elementary sighting instruments, such as the astrolabe and the sextant. Nevertheless, with this equipment, some profound conclusions were possible: for example, the Sun is further from us than the Moon, which orbits Earth; Earth is round; and with very careful observation, one can deduce that the Sun, not Earth, is the likely center of motion in the solar system, a theory first published widely by Nicolaus Copernicus in 1543.

The latter idea required a huge leap of intuition. After all, our unaided eyes don't have enough resolving power to distinguish the other planets from true point sources: there is nothing to indicate that those apparently tiny points of light have anything in common with the great sphere we live on.

It also impinged on religious faith, as Galileo found to his detriment when in 1610 he published his treatise Sidereus Nuncius (The Starry Messenger). Made with the newly invented telescope, his observations of the motions of Jupiter's largest moons and the phases of Venus provided the first powerful evidence in support of the Copernican theory. The religious establishment of the time, unable to accept the notion that man was not at the center of the cosmos, placed Galileo under house arrest for much of the rest of his life. But nothing could stop the revolution in thinking that would take place, fueled by observations made with resolving power and sensitivity an order of magnitude greater than had ever been possible before.

Today, another revolution is under way. Modern telescopes capture as much as 40 000 times more light than Galileo's original, making them much more sensitive to faint objects. But until recently, their resolving power has been limited by Earth's atmosphere, so that the images they make are only a few times sharper than those Galileo saw. Now, however, the technology of adaptive optics is yielding images at the theoretical limit of sharpness, finally allowing astronomers to capitalize on the full potential of the world's biggest telescopes.

—M.L-H.