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changed his mind about those hundreds of “new universes.” A new observation forced him to reconsider his previous assertions. It happened on a cold November evening in 1790 when Herschel came upon an eighth-magnitude star that was surrounded by a faintly luminous atmosphere of considerable extent. “A most singular phænomenon!” he jotted down in his notebook. He called this haze a “planetary nebula” because of its resemblance to a planetary disk (as noted earlier, now known to be an aging star shedding its outer envelope of gas). “Cast your eye on this cloudy star,” he wrote, “and the result will be no less decisive…that the nebulosity about the star is not of a starry nature… Perhaps it has been too hastily surmised that all milky nebulosity, of which there is so much in the heavens, is owing to starlight only.” In Herschel's mind, nebulae had to be comprised of either stars or a “shining fluid”—not both. So he decided that any nebulae that remained unresolved through his telescope were no longer distant stellar systems, but instead collections of luminous matter, likely the stuff out of which stars ultimately condensed.

Herschel's telescopes were so much better than the equipment of any other astronomer at the time that his colleagues trusted his judgment on this matter. They simply didn't have the telescopic power to confirm his findings. As a result, Herschel's pronouncement became the accepted wisdom. The universe swiftly shrank back to the borders of the Milky Way. We were alone in the universe once again … at least for a while.

Throughout the nineteenth century, the two explanations for the unresolved nebulae went through a relentless tug-of-war, one side winning the hearts of astronomers for a time, then the other. Some insisted they were nearby clouds of gas, while others championed them as far-off islands of stars. Each faction was seeking a solitary explanation, simple and elegant—and that meant choosing between the two possible options.

Cosmology at this time continued to be of more interest to independent astronomers than the professionals who toiled at university-or government-sponsored observatories, and it was one of these self-directed observers who gave renewed hope to those who favored the idea that the dim nebulae were similar to the Milky Way, separate galaxies whose individual stars over the vast distances melted into a uniform pool of light. The excitement arose when William Parsons, the third Earl of Rosse, constructed a giant telescope on the grounds of his ancestral home, Birr Castle, in central Ireland, seventy miles west of Dublin. So big was the telescope tube that at the observatory's opening ceremony, a dean of the Church of Ireland walked right down the huge cylinder wearing a top hat and an open umbrella.

Young Rosse (then Lord Oxmantown, prior to succeeding his father in the earldom) served in the British Parliament, but his passion was telescope-building, with his decided aim, according to those who knew him, “to make a telescope of the largest dimensions possible with the resources of his time.” In 1834, at the age of thirty-four, Rosse left politics to devote himself to a newfound career as a gentleman scientist. He had long wanted to surpass Herschel's instruments in size and devised the methods himself for casting and polishing the metal mirror in his own workshops, personally training the laborers on his estate to assist him. Though an aristocrat, he put on no airs; a British reporter once caught him working at a vise, his shirtsleeves rolled up, displaying brawny arms. The mirrors he constructed were made out of a tin and copper alloy, a blend that resulted in a reflectivity almost as high as silver. Rosse's first big success was a three-foot-wide mirror mounted in a tube twenty-six feet long. “It is scarcely possible to preserve the necessary sobriety of language in speaking of the moon's appearance with this instrument,” reported a friend.

The triumph gave Rosse the confidence to construct a mirror twice the size, taking no notice that the Irish weather was more infamous for