Coming of Age in the Milky Way - Timothy Ferris (2003)

Part I. SPACE

Chapter 8. DEEP SPACE

The infinitude of the creation is great enough to make a world, or a Milky Way of worlds, look in comparison with it what a flower or an insect does in comparison with the earth.

—Immanuel Kant

I have looked farther into space than ever [a] human being did before me.

—William Herschel

           Bright nebulae (from the Latin for “fuzzy”) are diffuse patches of glowing material found scattered here and there among the stars. Most can be seen only with a telescope. Although they resemble one another superficially, the bright nebulae actually comprise three very different classes of objects. Some, misnamed “planetary” because they are spherical in shape and bear a passing resemblance to planets, are shells of gas thrown off by old, unstable stars; a typical planetary nebula is about one light-year in diameter and has one-fifth the mass of the sun. Others, the reflection and emission nebulae, are clouds of gas and dust illuminated by nearby stars; in many cases, the stars doing the illuminating have themselves recently condensed from the surrounding cloud. These nebulae measure hundreds of light-years in diameter and can harbor the mass of a million or more suns. They represent the bright, congealed parts of the still more extensive dark nebulae that wend their way throughout much of the disk of the Milky Way galaxy —though this was not recognized at first, since the dark nebulae are too inconspicuous to call attention to themselves. Finally there are the elliptical and spiral nebulae. These are galaxies in their own right, millions of light-years away. A major galaxy can measure over one hundred thousand light-years in diameter and contain hundreds of billions of stars.

In much the same way that human beings could not investigate interstellar space until we understood that the sun is one among many stars, so the realization that we live in a universe of galaxies, scattered across immense gulfs of space, required that we first understand the nature of the nebulae. This involved comprehending not only the appearance of the nebulae but also their chemical composition, an effort that spawned the sciences of spectroscopy and astrophysics.

Science is said to proceed on two legs, one of theory (or, loosely, of deduction) and the other of observation and experiment (or induction). Its progress, however, is less often a commanding stride than a kind of halting stagger—more like the path of the wandering minstrel than the straight-ruled trajectory of a military marching band. The development of science is influenced by intellectual fashions, is frequently dependent upon the growth of technology, and, in any case, seldom can be planned far in advance, since its destination is usually unknown. In the case of the exploration of intergalactic space, the first step was taken by armchair theorists—by the philosopher Immanuel Kant and the mathematician Johann Lambert—followed by the observations of the prescient amateur astronomer William Herschel.

When Kant first wrote on cosmology he was not yet Kant, the intellectual titan whose unification of empiricism and rationalism was to illuminate and enliven philosophy throughout the world. The year was 1750, and he was but twenty-six years old. The death of his father four years earlier had obliged him to interrupt his education, and he was working as a private tutor in East Prussia. He had earned a bachelor’s degree (paying his tuition out of his earnings from gambling at billiards and cards) but five more years would pass before he was awarded his doctorate. He had not yet ruined his writing style by trying to satisfy the formal requirements established by the philosophy faculty at the University of Königsberg, where, at the age of forty-six, he would finally be appointed professor of logic and metaphysics. He was a witty, outgoing man and attractive to women, though he could never bring himself to marry. A creature of habit, he ate one meal a day, always with friends, consulted a barometer and thermometer by his bedside each morning in order to determine how to dress, and took his evening walk so punctually that neighbors literally set their clocks by his appearance on the street. He taught mathematics and physics, revered Lucretius and Newton, and read everything from theological history to the actuarial tables.

One day Kant read, in a Hamburg journal, a review of a book titled An Original Theory or New Hypothesis of the Universe, by an English surveyor and natural philosopher named Thomas Wright. Wright in his piety had taught himself astronomy the better to appreciate the grandeur of God’s creation, and his books and lectures, freighted with moral and theological lessons, were popular in society circles. In the course of a variegated career, Wright proposed a number of models of the universe, many of them contradictory and all burdened with such concerns as the location of the throne of God, which he put at the center of the cosmos, and hell, which he relegated to the outer darkness.

The cosmological speculations of such a thinker might not normally have commanded the attentions of a Kant, but the summary of Wright’s book that Kant read distorted Wright’s theories, and, in the process, improved upon them. The result was one of journalism’s signal contributions to cosmology, the inadvertent promotion of a nonexistent hypothesis that Kant then turned into this world’s first glimpse of the universe of galaxies.

Wright, following the same erroneous route that had misled Plato, Aristotle, Ptolemy, and Copernicus, assumed the universe to be spherical. But where his pre-Copernican predecessors had put the sun at the center of the universe, Wright suggested that the sun instead belongs to the celestial sphere. What he had done, really, was to resurrect the starry sphere of Aristotle and Ptolemy, but with the sun as one of its stars. Wright’s cosmos was hollow, like an orange with the pulp sucked out and with the sun and other stars in the skin. Wright noted that the appearance of the Milky Way as a band of stars in the sky might be explained as our view of this starry shell from our location within it: When we look along a line tangential to the sphere we see many stars—the Milky Way—and when we look along the sphere’s radius we see relatively few stars.

The synopsis that Kant read in the newspaper stressed this last point—happily, the most felicitous part of Wright’s theory—and was vague about the rest. Consequently, Kant got the mistaken impression that Wright’s universe consisted of a flattened disk of stars, like a thumbnail-sized slice cut tangentially from the skin of an orange. Kant therefore supposed (as he thought Wright had also) that the stars of the Milky Way are arrayed across a disk-shaped volume of space. So excited was Kant about this idea that he wrote a book on it. He stated its thesis this way:

Just as the planets in their system are found very nearly in a common plane, the fixed stars are also related in their positions, as nearly as possible, to a certain plane which must be conceived as drawn through the whole heavens, and by their being very closely massed in it they present that streak of light which is called the Milky Way. I have become persuaded that because this zone, illuminated by innumerable suns, has almost exactly the form of a great circle, our sun must be situated quite near this great plane. In exploring the causes of this arrangement, I have found the view to be very probable that the so-called fixed stars may really be slowly moving, wandering stars of a higher order.1

From this precarious foothold Kant made a cat’s leap to the universe of galaxies. He knew from reading of the observations of the French astronomer Pierre-Louis de Maupertius that elliptical nebulae had been found here and there in the sky. One of these, the Andromeda nebula, could be seen with the unaided eye; others were discernible through telescopes. Kant realized that if the universe were composed of many disk-shaped aggregations of stars—galaxies, as we would say today—then the elliptical nebulae could be other galaxies of stars like our Milky Way. “I come now to that part of my theory which gives it its greatest charm, by the sublime idea which it presents of the plan of the creation,” he wrote.

If a system of fixed stars which are related in their positions to the common plane, as we have delineated the Milky Way to be, be so far removed from us that the individual stars of which it consists are no longer sensibly distinguishable even by the telescope; if its distance has the same ratio to the distance of the stars of the Milky Way as that of the latter has to the distance of the sun; in short, if such a world of fixed stars is beheld at such an immense distance from the eye of the spectator situated outside of it, then this world [i.e., the Milky Way galaxy] will appear under a small angle as a patch of space whose figure will be circular if its plane is presented directly to the eye, and elliptical if it is seen from the side or obliquely. The feebleness of its light, its figure, and the apparent size of its diameter will clearly distinguish such a phenomenon when it is presented from all the stars that are seen single.2

Wright envisioned the universe as a bubble, and proposed that the appearance of the Milky Way in the sky represented our view of its starry skin. Kant was unaware of the first part of his argument, but seized upon the second, correctly conceiving of the sun as belonging to a flattened system of stars—a galaxy.

Kant realized that disk-shaped galaxies, viewed at random angles, would produce the appearance of seemingly round, oval, and linear “nebulae.”

The elliptical nebulae, Kant wrote, present us with just such apparitions. The nebulae are “systems of many stars” lying “at immense distances.”3 Here for the first time was a portrait of the universe as consisting of galaxies adrift in the vastness of cosmological space.

Kant’s book, titled Universal Natural History and Theory of the Heavens, was published—if that is the word—in 1755, but its publisher immediately went bankrupt, the books were seized to satisfy his debts, and the world, consequently, heard little of it. Kant dedicated it to Frederick the Great, but many better-known artists and philosophers were dedicating their works to this singularly enlightened monarch—Johann Sebastian Bach, for one, had recently composed his Musical Offering in Frederick’s honor—and the king never saw Kant’s book.

Frederick did, however, come upon the idea of a universe of galaxies, by another and even less likely avenue. His acquaintanceship with it began one evening in March 1764 when he entered a darkened room, nearly all its candles extinguished, to interview, for membership in the Berlin Academy of Sciences, a candidate whose appearance and manner were so off-putting that the friends who had arranged the meeting had feared that Frederick would never admit him if he could see him clearly.

The man in the dark was Johann Heinrich Lambert, and his friends had ample grounds for their concern. Lambert’s appearance was unsettling: His forehead was so high that most of his face stood above, not below, the eyebrows, and he dressed uniquely, in a scarlet tailcoat, turquoise vest, black trousers and white stockings, an outfit to which, on special occasions, he added a broad ribbon tied in two bows, one adorning his pigtail and the other his chest. Though his eyes were piercing he seldom looked directly at anyone, preferring, instead, to strike a profile. If an interrogator tried to step around to get a look at him, Lambert would turn slowly on his heel, maintaining the profile, a human moon.

“Would you do me the favor,” said Frederick to the darkling Lambert, “of telling me in what sciences you are specialized?”

“In all of them,” Lambert replied, addressing a point in space ninety degrees away from the king.

“Are you also a skillful mathematician?” asked Frederick.

“Yes.”

“Which professor taught you mathematics?”

“I myself.”

“Are you therefore another Pascal?” asked Frederick, referring to the great mathematician of the previous century.

“Yes, Your Majesty,” replied the voice in the dark.4

Frederick turned away, barely able to contain his laughter, and left the room. That night at dinner he remarked that he had just met the biggest blockhead in the world. But Lambert, when consoled by his friends on the outcome of the interview, serenely assured them that he would get the appointment, since should Frederick “not name me, it would be a blot in his own history.”5 And, indeed, following a review of his publications, Lambert was appointed to the Academy.

Among his works was a collection of essays titled Cosmological Letters, which this solitary man, so freakish-looking that children followed him through the streets as they might a fakir in a loincloth, had written as a series of letters to an imaginary friend. In it, Lambert proposed that the sun lies toward one edge of a disk-shaped system of stars, the Milky Way, and that there are “innumerable other Milky Ways.”6 He indicated that he had arrived at this theory while gazing for long hours at the night sky:

I sat at the window and as the objects on Earth put aside all their charm to draw attention, there still remained for me the starry sky as, of all showplaces, the most worthy of contemplation. … I take on wings of light and soar through all spaces of the heavens. I never come far enough and the desire always grows to go still farther. In such reflections did I present to myself the Milky Way…. This luminous arch, which stretches all around the firmament and decorates the world like a ring studded with gems, roused in me astonishment and wonderment.7

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.”8 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.9

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.10 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.”11

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.”12

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.”13 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.”14

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.”15

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.

I have tried to improve telescopes and practiced continually to see with them. These instruments have played me so many tricks that I have at last found them out in many of their humours and have made them confess to me what they would have concealed, if I had not with such perseverance and patience courted them.16

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.17 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.”18

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.

The largest telescope in the world was built, therefore, with the king’s money, by a team of workmen under Herschel’s direction. It had a forty-eight-inch mirror that weighed a ton, housed in a tube forty feet long. To reach the eyepiece, Herschel had to climb a scaffolding that rose fifty feet into the air. Oliver Wendell Holmes described the instrument as “a mighty bewilderment of slanted masts, spars and ladders and ropes, from the midst of which a vast tube … lifted its mighty muzzle defiantly towards the sky.”19 At its dedication, the king took the archbishop of Canterbury by the arm with the words, “Come, my Lord Bishop, I will show you the way to Heaven.”20

With the forty-eight-inch reflector, Herschel discovered Enceladus and Mimas, the sixth and seventh satellites of Saturn, but ultimately the heroic telescope proved to be a disappointment. Training it on a given piece of sky was a taxing process that involved shouting instructions down to a team of laborers stationed in the rigging below, and its mirror tended to warp and mist over with changes in temperature and humidity. Herschel soon returned to working with smaller telescopes he had built by hand.

The nebulae continued to fascinate him. In 1781 he received a copy of Charles Messier’s new catalog of these glowing islands of light, promptly set to work observing them, and found that “most of the nebulae … yielded to the force of my light and power, and were resolved into stars.” He concluded, prematurely, that all nebulae were but star clusters, and could be resolved into their constituent stars once large enough telescopes were employed in observing them. His confidence in this comprehensive but erroneous hypothesis was shaken by his subsequent investigations of what he labeled the “planetary” nebulae—the ones now known to be shells of gas ejected by stars. When Herschel observed planetary nebulae in which the central star was too dim to be seen, he assumed that they were globular star clusters. But then, on the night of November 13, 1790, he came upon a planetary nebulae in Taurus with a clearly visible central star. He appreciated its significance immediately. “A most singular Phaenomenon!” he wrote in his journal. “A star of about the eighth magnitude, with a faint luminous atmosphere…. The star is perfectly in the center and the atmosphere is so diluted, faint and equal throughout, that there can be no surmise of its consisting of stars; nor can there be a doubt of the evident connection between the atmosphere and the star.” He decided that some nebulae must, after all, be composed not of stars but of “a shining fluid” of unknown constitution. “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,” he wrote, modifying his earlier hypothesis. “What a field of novelty is here opened to our conceptions!” he exclaimed, more delighted by the variety of the sky than bothered at having been wrong.21

Herschel could be astonishingly acute. He called the Orion Nebula, a knot of congealing gas sixteen hundred light-years from Earth, “the chaotic material of future suns,” which is exactly what it is.22 He argued that the sun belongs to a vast cluster of stars—a galaxy, as we would say today—and he tried to map its boundaries, by counting stars of various magnitudes in various directions in the sky. This effort failed, owing both to the fact that apparent magnitude is not a reliable index to the distance of stars and to the presence of dark, obscuring nebulae in the Milky Way that Herschel mistook for empty space. Nonetheless the inspiring fact remains that an oboe player with a handmade telescope undertook, in the eighteenth century, a scientifically defensible project aimed at charting the extent of the entire Milky Way galaxy.

Herschel studied other galaxies, too, notably the great nebula in Andromeda, which he assumed, correctly, to glow with “the united luster of millions of stars.” He even noted that the central part of Andromeda was of “a faint red color.” The central region of this giant galaxy is, indeed, warmer in hue than the surrounding disk—it consists of old red and yellow stars, while young blue stars predominate in the surrounding disk—but it seems incredible that this distinction, which was not fully established until the twentieth century, could have been detected by the eye of an eighteenth-century astronomer. And yet, Herschel being Herschel, one sometimes wonders.

In any case, Herschel’s legacy has less to do with the extent to which his conclusions were right or wrong than with his prophetically modern approach to deep-space astronomy. At a time when most astronomers were peering at planets through the narrow fields of refracting telescopes, Herschel was harvesting great swaths of ancient light from distant nebulae and galaxies. While they were refining their estimates of distances within the solar system to the second decimal place, he was endeavoring to chart the starshoals of intergalactic space. While they were using estimates of the velocity of light to adjust their calculations of the orbits of the satellites of Jupiter, he was, he realized, seeing so far into space as to be viewing the universe as it looked millions of years in the past. Herschel’s use of large reflecting telescopes to discern what he called “the construction of the heavens” may have been technologically precipitate, but it presaged the methods of the twentieth-century astronomers who were to realize his dreams. Cosmology for Kant and Lambert had been principally an indoor discipline; Herschel took it outdoors.

Sustained by his love for what he called “this magnificent collection of stars” in which we live, Herschel kept working until the end. “Lina, there is a great comet,” he wrote his sister Caroline on July 4, 1819. “I want you to assist me. Come to dine and spend the day here. If you can come soon after one o’clock we shall have time to prepare maps and telescopes. I saw its situation last night, it has a long tail.”23 He was eighty years old at the time, and he was still at work when he died, two years later.

William Herschel sought to chart our galaxy by counting stars of given apparent magnitudes in all quarters of the sky (top). The resulting chart (bottom), though extremely rough, hinted at the existence of the galactic plane.