Stargazer: The Life and Times of the Telescope by Fred Watson. Da Capo Press, $24.95, 349 pages.

San Francisco Chronicle

August 14, 2005

Looking into outer space, ever more clearly

By PHILLIP MANNING

I wasn't sure the world needed another history of the telescope until I read Fred Watson's "Stargazer." With good-natured prose, Watson, chief of Australia's Anglo-Australian Observatory, leads the reader smoothly from Hans Lipperhey's primitive 1608 invention to today's incredibly sophisticated telescopes, enlivening the history with tidbits of unlikely lore.

For example, during the first three years of its existence, the telescope had no name and was known only as "the invention to stretch out sight." We also learn that the famed astronomer Edwin Hubble had a mean streak that prompts Watson to sum up his life as "you don't have to be nice to become immortal." Richard Panek's 1988 history "Seeing and Believing" is more about advancements in astronomy than the improvements in telescopes that made those advances possible. Watson is interested in the instruments themselves, and he writes lovingly of each bold new design: Galilean refractors, Newtonian reflectors, Herschel's squat 40-foot giant. And he shows how, over 400 years, instrument makers solved the problems posed by each new design.

A particularly vexing one was chromatic aberration. When ordinary white light passes through a lens, it bends each color that makes up the light by a slightly different amount, blue more than red. Thus, blue light is focused slightly closer to the lens than red. This blurry focus transforms stars into colorful fuzzy images of little use to astronomers.

One way around this was to eliminate the objective lens in the refracting telescope, as Isaac Newton did, creating the reflecting telescope in which a mirror replaces the image-blurring lens. But casting and polishing the metal mirrors caused problems, too. One 19th century astronomer, working with a poorly polished reflector, reported "such absurdities as egg-shaped protuberances from the planet Jupiter and a Saturn-like ring around Mars." Problems like these with reflecting telescopes kept craftsmen scrambling to improve refracting telescopes.

One route to minimize chromatic aberration was to make telescopes longer. Isaac Newton summed up the situation: "I do not yet see any other means of improving Telescopes by Refractions alone, than that of increasing their lengths." And that is what telescope makers did. The earliest telescopes were about 1 foot long, and Galileo's best measured only 5 feet. By the middle of the 17th century, a good one was 14 feet long. And they kept growing: 23 feet, 60 feet, a 150-footer built in 1670 and finally an ungainly 210-foot-long monster suspended from a tall mast. Looking back to the era of long telescopes, Watson writes, "is like looking back to the age of dinosaurs."

That era ended in the 18th century with the invention of a two-element lens made of a clever combination of glasses that minimized chromatic aberration. But another race for size would soon begin -- this one aimed at making larger mirrors for reflecting telescopes. It began when astronomers realized they needed bigger mirrors for greater light-gathering capacity to observe more distant objects. The most heralded achievement in this race was the completion in 1948 of the great 200-inch mirror for the Hale telescope on Mount Palomar in Southern California.

What astronomers learned thanks to these improvements was not always what we wanted to hear. First, they discovered just how unimportant we and our planet are. We are not the center of the universe, as Aristotle proclaimed. In fact, we are just one insignificant planet revolving around one of the 100 billion stars in the Milky Way, which is itself just one of 100 billion galaxies.

Not only are we less important than we thought, we are also lonelier. In the 1990s, astronomers' telescopes revealed that the universe was expanding at an accelerating rate, when most scientists had thought gravity would slow the rate of expansion. This disturbing new finding means that the stars will forever recede from us at an increasingly rapid pace, isolating us in the cold darkness of space.

Development continues. A new generation of telescopes with huge mirrors composed of smaller mirrors whose position is controlled by computers promises to let us see even farther into space, where we may detect Earth-sized planets elsewhere in the universe. Maybe astronomers will find we have neighbors with whom we can share the darkness.
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