Coming of Age in the Milky Way (22 page)

The galactic rhapsodies of Kant and Lambert helped awaken the human mind to the potential richness and reach of the universe. But rapture in itself, no matter how insightfully founded, is of course an inadequate foundation upon which to ground a scientific cosmology. To determine whether the universe is in fact comprised of galaxies would require actually mapping the universe in three dimensions, by means of observations more exacting, if no less enchanting, than Lambert’s meditative stargazing.

The point man of this observational campaign was William Herschel, the first astronomer to make acute, systematic observations of the universe beyond the solar system, where lies the vast majority of everything there is. Herschel was born in Hanover on November 15, 1738, the son of a musician with an active intellect who taught his six children to think for themselves, inciting heated dinner-table discussions of science and philosophy and taking them outdoors on clear nights to teach them the constellations. The Seven Years’ War found the eighteen-year-old Herschel playing oboe in his father’s unit, the Hanoverian Guards’ band. Mars hates music, and the band was superfluous in battle. “Nobody had time to look after the musicians,” Herschel recalled, in his deadpan way. “They did not seem to be wanted.”
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For a time he wandered through the carnage in a state of abstraction worthy of Buster Keaton in
The General
. Then one day, when French troops got within firing range of the muddy field where the band was encamped, Herschel’s father advised his son on the better part of valor, and the boy obediently walked out of the war. “Nobody seemed to mind,” he noted.
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He fled to England, where the king at the time was the politically
disinterested but indisputably Hanoverian George II, and there flourished. Herschel’s English was excellent, his manner refreshingly direct and personable; “I have the good luck to make friends everywhere,” he wrote home.
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He continued his education by reading constantly; many years later he would tell his son John that once while reading on horseback he suddenly found himself standing on the road, book still securely in hand, the horse having tossed him in a perfect somersault though the air. His mind was sufficiently powerful to impress the likes of David Hume, yet he wore his learning lightly enough to thrive in London society. His musical fortunes benefited from the example set by his distinguished countryman George Frederick Handel, and by age thirty Herschel had been appointed organist of the chapel at Bath, a genteel post where he could expect to abide in comfort all the rest of his days.

Instead, he felt dissatisfied. Music was not enough; he knew he was no Handel, and was not content with mere facility. “It is a pity that music is not a hundred times more difficult as a science,” he wrote. “… My love of activity makes it absolutely necessary that I should be busy, for I grow sick by idleness; it kills me almost to do nothing.”
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He found deliverance by following Kepler’s and Galileo’s path across the bridge that leads from music to astronomy. Like many amateur astronomers before and since, he began by reading books of popular science. He was particularly impressed by James Ferguson’s
Astronomy Explained Upon Sir Isaac Newton’s Principles
and Robert Smith’s
A Compleat System of Opticks
.

Ferguson had begun his study of astronomy when as an uneducated shepherd boy he used to lie on his back in the fields of Scotland at night and measure the angles between stars with beads positioned on a thread. He taught himself to read, became a teacher and popular lecturer, wrote two well-received books on astronomy, and ultimately was elected to the Royal Society. It was in Ferguson’s book that Herschel first read about the nebulae. Some nebulae appeared to be starless; as Ferguson wrote, “There are several little whitish spots in the Heavens, which appear magnified and more luminous when seen through a telescope; yet without any stars in them. One of these is in Andromeda’s girdle.” Other nebulae were tangled in stars. “They look like dim stars to the naked eye,” wrote Ferguson, “but through a telescope they appear [to be] broad illuminated parts of the sky; in some of which is one star, in others
more…. The most remarkable of all the cloudy stars is that in the middle of Orion’s sword.”
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The Milky Way galaxy, seen edge-on, is disklike in shape, with an elliptical central region. The disk is surrounded by a halo of globular star clusters and old stars.

In Smith’s book, Herschel read that although the stars—and, presumably, the nebulae—are distant, the immense spaces they inhabit may be penetrated by using large telescopes: More stars can be seen, Smith wrote, “as the aperture is more enlarged to take in more light.”
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Herschel took this lesson utterly to heart. His career was one long epitomization of the principle that telescopes enable us to see
into
space, and that the larger the telescope, the farther we can see.

Herschel began by purchasing a refracting telescope, but he soon found, as Newton had, that it suffered from chromatic aberration, meaning that it tended to introduce false colors. This defect eventually would be overcome by the development of compound apochromatic lenses, but at the time Herschel got into astronomy
the only way to avoid it in refracting telescopes was to make them with very long focal lengths. This situation had driven observers to extremes. John Flamsteed erected a refractor 90 feet long at the Royal Greenwich Observatory, and Cassini in Paris studied Saturn through a series of ever more ambitiously constructed telescopes with focal lengths of 17, 34, 100, and 136 feet. Since a rigid tube of such a length could scarcely be constructed, much less mounted successfully, the tube often was done away with, and the objective lens was instead mounted on the highest available platform, such as the roof of a tall public building or, in the case of James Pound of England, on a maypole in Wanstead Park. The observer stood several city blocks away, eyepiece in hand, and sighted on the distant lens, awaiting the few precious moments when the planet Jupiter or the binary star Epsilon Lyrae would swim across his field of view. An astronomer blessed with great patience could, occasionally, make useful observations with
such a contraption—Bradley in 1722 managed to measure the angular diameter of Venus using a tubeless refractor 212 feet long—but most found such reedy spyglasses so unwieldy that the cure was worse than the disease. Herschel constructed refractors with focal lengths of 4, 12, 15, and 30 feet, then gave up on them. “The great trouble occasioned by such long tubes, which I found it almost impossible to manage, induced me to turn my thoughts to reflectors,” he wrote. He rented a small reflecting telescope of the sort invented by Newton, and found it “so much more convenient than my long glasses that I soon resolved to try whether I could not make myself such another.”
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The spiral arms of the Milky Way galaxy are produced by the light of millions of fiercely burning young, giant stars.

This decision marked the beginning of extragalactic astronomy, and the end of Herschel’s leisure. Soon he was at work in every free hour, casting metal mirrors and laboriously grinding them to the precise concave figure required to bring starlight to a sharp focus. His sister Caroline—who had joined him in England in hopes of singing with the orchestra, but found instead that their lives were being given over to astronomy and their home turned into an optics shop—helped out by reading to him and feeding him sandwiches while he ground and polished mirrors for up to sixteen hours at a stretch. With a delicacy of touch that he attributed to his boyhood training as a violinist, Herschel fashioned hardwood telescope tubes as elegant as cellos and topped them off with magnifying eyepieces made of cocus, the wood used in oboes like the one he had played as a boy. Less than ten years after he opened his first astronomy books, he could boast confidently “that I absolutely have the best telescopes that were ever made.”
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Herschel’s skill as an observer was equally refined; he had a way with telescopes. “Seeing is in some respect an art, which must be learnt,” he wrote.

With the ardor of a man possessed, Herschel stayed at the telescope on virtually every clear night of the year, all night long,
taking only a few minutes off every three or four hours to warm himself—or, as happened one night when the temperature dropped to 11 degrees Fahrenheit, to fetch a tool to break through the ice that had glazed over his inkwell. He rushed to the telescope to observe during intermissions in the concerts he conducted at Bath. When skies were cloudy he and Caroline waited up, hoping for a change in the weather. “If it had not been for the intervention of a cloudy or moonlit night I know not when he or I either would have got any sleep,” wrote Caroline in her diary.
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When they moved to Datchet, to a dank house so near the Thames that the yard was often flooded, Herschel waded through the water and climbed to the eyepiece of the telescope, staving off ague by rubbing onion on his hands and face. “He has an excellent constitution,” wrote Caroline, “and thinks about nothing else in the world but the celestial bodies.”
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Herschel’s preferred method of observing consisted of “sweeping” the sky. Wearing a black hood to keep any stray light from dazzling his dilated, dark-adapted eyes, he would move the telescope across a segment of sky, pausing to note the locations of interesting objects, then move the telescope slightly in the perpendicular and sweep back along an adjacent path. Ten to thirty such oscillations he called a sweep; and he registered each in what he called his “Book of Sweeps.” This was making a virtue of necessity; his telescope lacked the equatorial mountings and clock drives that are employed today to compensate for the earth’s rotation and to hold a single object effortlessly in view. Its great advantage was that it encouraged Herschel to memorize whole swathes of sky; the most significant northern hemisphere star map of the later eighteenth century may well have existed not on the pages of a celestial atlas but in Herschel’s mind.

It was to this familiarity with the sky that Herschel owed his discovery, on the night of March 13, 1781, of the planet Uranus. Uranus had been glimpsed dozens of times before, by Bradley, Flamsteed, and others, but always had been mistaken for a star. Herschel, his mind an encyclopedia of the night sky, realized as soon as he saw it that no star belonged there. At first he mistook the little green dot for a comet, but the Astronomer Royal, Nevil Maskelyne, calculated its orbit and determined that it must be a planet, one far beyond Saturn. In a single stroke, Herschel had doubled the radius of the known solar system. The resulting fame
brought him a fellowship in the Royal Society, a pension, and an appointment as astronomer to King George III—who was being blamed for losing the American Revolution and was suffering a mental breakdown at the time, and must have felt grateful for a little good news.

Herschel received a royal grant of four thousand pounds to build and operate what would be the world’s largest telescope. Out of his own funds he had already managed to build a reflector twenty feet long, with a mirror eighteen and a half inches in diameter, but there were clear signs that he had pushed his private efforts about as far as they could go. Most ominous was the episode of the horse-dung mold. Herschel had wanted to cast a mirror fully three feet in diameter, with three times the light-gathering power of the eighteen-inch. No foundry would take on the unprecedented project, so Herschel resolved to do it himself, in the basement of his house at 19 New King Street in Bath. He constructed an inexpensive mold out of what the uncomplaining Caroline described as “an immense quantity” of horse dung. She, William, and their brother Alex took turns pounding the dung, assisted by their friend William Watson of the Royal Society. Finally came the day to, as Herschel put it, “cast the great mirror.” At first all went well, but then the mold cracked under the intense heat and molten metal flowed out across the floor, exploding flagstones and sending them caroming off the ceiling. The party fled into the garden, pursued by a rapidly expanding pool of liquid metal. Herschel took refuge on a pile of bricks and there collapsed. He had reached the practical limits of amateur telescope making.