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Cosmology

 

Cosmology and Astronomy

Horizons: Exploring the Universe, 11th Edition by Michael A. Seeds, and Dana Backman (Brooks Cole) This newly revised and updated Edition of HORIZONS shows readers their place in the universe, not just their location, but also their role as planet dwellers in an evolving universe. Fascinating and engaging, the book illustrates how science works, and how scientists depend on evidence to test hypotheses. Students will learn to focus on the scientific method through the strong central questioning themes of "What are we?" and "How do we know?"

Excerpt: Every chapter has been reorganized to focus on the two main themes of the book. The What Are We? boxes at the end of each chapter provide a personal link between human life and the astronomy in that chapter, including, for example, the origin of the elements, the future of exploration in the solar system, and the astronomically short span of our civilization.

The How Do We Know? boxes have been rewritten to be more focused on helping you understand how science works and how scientists think about nature.

Every chapter has been rewritten to place the "new terms" in context for you rather than as a vocabulary list. New terms are boldfaced where they are first defined in the text of the chapter and reappear in context as boldface terms in each chapter summary. Those new terms that appear in Concept Art portfolios are boldfaced in the art and are previewed in italics as the portfolios are introduced.

Guideposts have been rewritten, shortened, and focused on a short list of essential questions that guide you to the key objectives of the chapter.

Every chapter has been updated to include new research, images, and the latest understanding, ranging from discoveries of how planets form in dust disks around young stars to the latest insights into the nature of dark energy.

Special Features

• What Are We? items are short summaries at the end of each chapter to help you see how you fit in to the cosmos.
• How Do We Know? items are short boxes that help you understand how science works. For example, the How Do We Know? boxes discuss the difference between a hypothesis and a theory, the use of statistical evidence, and the construction of scientific models.
• Concept Art Portfolios cover topics that are strongly graphic and provide an opportunity for you to create your own understanding and share in the satisfaction that scientists feel as they uncover the secrets of nature. Color and numerical keys in the introduction to the portfolios guide you to the main concepts.
• Guideposts on the opening page of each chapter help you see the organization of the book. The Guidepost connects the chapter with the preceding and following chapters and provides you with a short list of essential questions as guides to the objectives of the chapter.
• Scientific Arguments at the end of many text sections are carefully designed questions to help you review and synthesize concepts from the section. An initial question and a short answer show how scientists construct scientific arguments from observations, evidence, theories, and natural laws that lead to a conclusion. A further question then gives you a chance to construct your own argument on a related issue.
• Celestial Profiles of objects in our solar system directly compare and contrast planets with each other. This is the way planetary scientists understand the planets, not as isolated unrelated bodies but as siblings with noticeable differences but many characteristics and a family history in common.
• End-of-Chapter Review Questions are designed to help you review and test your understanding of the material. End-of-Chapter Discussion Questions go beyond the text and invite you to think critically and creatively about scientific questions.

This book also offers the following online study aids as optional bundle items or for separate purchase:

• Enhanced WebAssign. Assign, collect, grade, and record homework via the Web with this proven system, using more than 1,000 questions both from the text and written specifically for WebAssign. Questions include animated activities, ranking tasks, multiple-choice, and fill-in-the-blank exercises.
• Virtual Astronomy Labs. These online labs give you an exciting, interactive way to learn, putting some of astronomy's most useful instruments into your hands—precise telescope controls to measure angular size, a photometer to measure light intensity, and a spectrograph to measure Doppler-shifted spectral lines.

Our Journey together is over, but before we part company, let's ponder one final time the primary theme of this book humanity's place in the physical universe. Astronomy gives us some comprehension of the workings of stars, galaxies, and planets, but its greatest value lies in what it teaches us about ourselves. Now that you have surveyed astronomical knowledge, you can better understand your own position in nature.

To some, the word nature conjures up visions of furry rabbits hopping about in a forest glade. To others, nature is the blue-green ocean depths, and still others think of nature as windswept mountaintops. As diverse as these images are, they are all Earthbound. Having studied astronomy, you can see nature as a beautiful mechanism composed of matter and energy, interacting according to simple rules, forming galaxies, stars, planets, mountaintops, ocean depths, forest glades, and people.

Perhaps the most important astronomical lesson is that humanity is a small but important part of the universe. Most of the universe is probably lifeless. The vast reaches between the galaxies appear to be empty of all but the thinnest gas, and stars are much too hot to preserve the chemical bonds that seem necessary for life to survive and develop. It seems that only on the surfaces of a few planets, where temperatures are moderate, can atoms link together in special ways to form living matter.

If life is special, then intelligence is precious. The universe must contain many planets devoid of life, planets where sunlight has shined unfelt for billions of years. There may also exist planets on which life has developed but has not become complex, planets where the wind stirs wide plains of grass and rustles through dark forests. On some planets, creatures resembling Earth's insects, fish, birds, and animals may watch the passing days only dimly aware of their own existence. It is intelligence, human or alien, that gives meaning to the landscape.

Science is the process by which Earth's intelligence has tried to understand the physical universe. Science is not the invention of new devices or processes. It does not create home computers, cure the mumps, or manufacture plastic spoons—those are engineering and technology, the adaptation of scientific understanding for practical purposes. Science is the understanding of nature, and astronomy is that understanding on the grandest scale. Astronomy is the science by which the universe, through its intelligent lumps of matter, tries to understand its own existence.

As the primary intelligent species on this planet, we are the custodians of a priceless gift— a planet filled with living things. This is especially true if life is rare in the universe. In fact, if

Earth is the only inhabited planet, our responsibility is overwhelming. We are the only creatures who can take action to preserve the existence of life on Earth, and, ironically, our own actions are the most serious hazards.

The future of humanity is not secure. We are trapped on a tiny planet with limited resources and a population growing faster than our ability to produce food. We have already driven some creatures to extinction and now threaten others. We are changing the climate of our planet in ways we do not fully understand. Even if we reshape our civilization to preserve our world, the sun's evolution will eventually destroy Earth.

This may be a sad prospect, but a few factors are comforting. First, everything in the universe is temporary. Stars die, galaxies die; perhaps the entire universe will someday end. Our distant future is limited, and this assures us that we are a part of a much larger whole. Second, we have a few billion years to prepare, and a billion years is a very long time. Only a few million years ago, our ancestors were starting to walk upright and communicate. A billion years ago, our ancestors were microscopic organisms living in the oceans. To suppose that a billion years hence there will be beings resembling today's humans, or that humans will still be the dominant intelligence on Earth, or that humans will even exist, are ultimately conceits.

Our responsibility is not to save our race for all eternity but to behave as dependable custodians of our planet, preserving it, admiring it, and trying to understand it. That calls for drastic changes in our behavior toward other living things and a revolution in our attitude toward our planet's resources. Whether we can change our ways is debatable—humanity is far from perfect in its understanding, abilities, or intentions. However, you must not imagine that we, and our civilization, are less than precious. We have the gift of intelligence, and that is the finest thing this planet has ever produced.

We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.
—T S. Eliot, "Little Gidding"

Excerpt from "Little Gidding" in Four Quartets, copyright 1942 by T. S. Eliot and renewed 1970 by Esme Valerie Eliot, reprinted by permission of Harcourt, Inc. and Faber & Faber, Ltd.

The History of the Telescope by Henry C. King (Dover) unabridged republication of the work first published by Charles Griffin & Co., Ltd., High Wycombe, Buckinghamshire, England, 1955. Foreword by Sir Harold Spencer Jones. Preface. 196 black-and-white illustrations. Index. "This book is one that I can heartily recommend."
—Sir Harold Spencer Jones, F. R. S., formerly Astronomer Royal

A model of comprehensive scholarship, The History of the Telescope relates not only the stories of early inventors and astronomers but also the rarely recorded details of the instruments themselves and their makers. This remarkable chronicle covers many fields, including professional and amateur astronomy, optics, glass and lens technology, and the craft of the precision instrument.

Author Henry C. King bases his accounts primarily on first-hand sources—the letters, memoirs, papers, and treatises of the men who worked with telescopes. The great intellects (Roger Bacon, Galileo, Newton) and innovators (Tycho Brahe, Huygens, Hooke, Sir William Herschel) receive their due, along with lesser-known craftsmen and amateurs: the seventeenth-century Italian telescope makers Campani and Divini; the great London instrument artists Graham, Dolland, and Ramsden; and the experimenters Foucault and Brashear, whose contributions to mirror manufacture remain fundamental to all levels of astronomical endeavor. The modern-day successors of these men and their achievements bring this history to its conclusion in the mid-twentieth century, with profiles of the instruments still in use today.

A prime resource on the evolution of the telescope, this volume is magnifi­cently illustrated with nearly 200 portraits, diagrams, and photographs.

Many Skies: Alternative Histories Of The Sun, Moon, Planets, And Stars by Arthur R. Upgren (Rutgers University Press) What if Earth had several moons or massive rings like Saturn? What if the Sun were but one star in a double-star or triple-star system? What if Earth were the only planet circling the Sun?

These and other imaginative scenarios are the subject of Arthur Upgren’s inventive book Many Skies: Alternative Histories of the Sun, Moon, Planets, and Stars. Although the night sky as we know it seems eternal and inevitable, Upgren reminds us that, just as easily, it could have been very different.

Had the solar system happened to be in the midst of a star cluster, we might have many more bright stars in the sky. Yet had it been located beyond the edge of the Milky Way galaxy, we might have no stars at all. If Venus or Mars had a moon as large as ours, we would be able to view it easily with the unaided eye. Given these or other alternative skies, what might Ptolemy or Copernicus have concluded about the center of the solar system and the Sun?

This book not only examines the changes in science that these alternative solar, stellar, and galactic arrangements would have brought, it also explores the different theologies, astrologies, and methods of tracking time that would have developed to reflect them. Our perception of our surroundings, the number of gods we worship, the symbols we use in art and literature, even the way we form nations and empires are all closely tied to our particular (and accidental) placement in the universe.

Many Skies, however, is not merely a fanciful play on what might have been. Upgren also explores the actual ways that human interferences such as light pollution are changing the night sky. Our atmosphere, he warns, will appear very different if we have a belt of debris circling the globe and blotting out the stars, as will happen if advertisers one day pollute space with brilliant satellites displaying their products.

From fanciful to foreboding, the scenarios in Many Skies will both delight and inspire reflection, reminding us that ours is but one of many worldviews based on our experience of a universe that is as much a product of accident as it is of intention.

 

The Illustrated on the Shoulders of Giants: The Great Works of Physics and Astronomy by Stephen Hawking (Running Press Book Publishers) What natural laws rule the heavens? How do the planets move? What keeps them in orbit? These are questions humans have attempted to answer for thousands of years. It has taken scientists of bold vision and daring to bring forth the answers. In The Illustrated On the Shoulders of Giants, you will encounter five such visionaries: Nicolaus Copernicus, Galileo Galilei, Johannes Kepler, Isaac Newton, and Albert Einstein. What makes this book truly groundbreaking is that it includes the most relevant excerpts from the master works of each—giving you the opportunity to peer into the minds of genius and read exactly what these men thought. In this single volume, you will find excerpts from original papers from Albert Einstein, first published in The Principle of Relativity, plus abridged versions of On the Revolutions of Heavenly Spheres by Nicolaus Copernicus, Dialogues Concerning '[h o New Sciences by Galileo Galilei, Harmonies of the World (Book Five) by Johannes Kepler, and Principia by Isaac Newton.

These are the works that changed the course of science, ushering astronomy and physics out of the Middle Ages and into the modern world. As you read them, you will be able to trace the evolution of science from the revolutionary claim of Nicolaus Copernicus that the Earth orbits around the Sun to the equally revolutionary proposal of Albert Einstein that space and time are curved and warped by mass and energy. What few people realize is that Einstein built on a little-known theory of Galileo's called the principle of relativity—further evidence that science advances through a series of incremental changes.

The book tells a compelling story. As theoretical physicist Stephen Hawking notes in his introduction, "Both Copernicus and Einstein have brought about profound changes in the way we see our position in the order of things. Gone is our privileged place at the center of the universe, gone are eternity and certainty, gone are Absolute Time and Space."

This version of Giants is also fascinating because of the stories it tells—in words and pictures. Sandwiched between the master works are essays that will increase your understanding of who these men were, and their lasting contributions to physics and astronomy. Learn about Copernicus' unwavering commitment to truth over religious doctrine, despite his position as a Polish priest; Galileo's spirit of defiance; Kepler's family and financial woes; Newton's passionate feuds; Einstein's humble beginnings. And enjoy more than 125 full-color illustrations throughout. This beautifully illustrated, fascinating book will no doubt inspire awe, and provide a better understanding of the universe and man's place in it.

Cosmic Discoveries: The Wonders of Astronomy by David H. Levy (Prometheus) who felt the exhilaration of discovering a breathtakingly beautiful comet that would make history -- guides the reader through pivotal moments in astronomy that forever changed our conception of the universe and humanity's place within it.

Levy, who made one of the most startling celestial discoveries since the start of recorded history, writes from the unique vantage point of a discoverer of comets. With infectious enthusiasm, he and his wife, Wendee Wallach-Levy, give the reader a glimpse of the enthralling adventure of cosmic discovery through stories of the most famous and brilliant astronomers.

For example, Tycho Brahe's discovery of a supernova in 1572 planted the seeds of a new understanding of the universe as a changing realm. A generation later, Galileo's discovery of the moons of Jupiter, new worlds that refused to orbit the Sun, challenged the whole doctrine of the Earth as the center of the universe. In the twentieth century, Harlow Shapley pushed back the envelope opened by Galileo: If the Earth was not the center of the universe, neither was the Sun -- the center of our galaxy was much farther away. Edwin Hubble further proved that our galaxy was but a tiny part of an expanding universe.

Through the centuries, astronomical discoveries have streamlined our understanding of the fundamentals of the development of life here and perhaps elsewhere in the universe. The crash of Comet Shoemaker-Levy 9 drove home the point that comets not only carry the basic ingredients for life, they deposit those building blocks during collisions with the planets, including Earth, "once again forcing humanity to reassess its notions about how life began and if it has seeded itself elsewhere."

This fascinating book will excite and inspire all who have stared at the sky in awe and amazement

The Illustrated Encyclopedia of the Universe by Ian Ridpath (Watson-Guptill) offers a complete guide to our discovery and understanding of the Universe, exploring all the facets that make up this fascinating but complex Subject.

Beginning with a History of Astronomy, it traces  the growth of the science from earliest times to the present day The essential ingredients to understanding the way everything in the Universe works-from the very large to the inconceivably small-are explained in The Laws of Physics and In Search of Quantum Reality. The birth of the Universe in the Big Bang is traced back to the first few seconds in The Universe: Past, Present and Future, which also looks at its evolution and raises the question Where will it all end. Contents of the Cosmos examines the phenomenon of this vast and mysterious World, the factors we understand and some that still defy explanation, from stars and galaxies to black holes. Horning in on our own small corner of the Universe, Our Solar System looks at the Sun and each of the planets. An introduction to professional and amateur astronomy is followed by a series of star charts, opening up the night sky to the reader, in Watching the Sky. The encyclopedia concludes with a comprehensive survey of the advances made in Space Exploration, from the first crude    - rockets, through the drama of the Space Race and the Moon landing, to the plans for a mission to Mars. In addition, six themes run throughout the book, covering key people and milestone events, dealing with major concepts and theories, and offering practical information on astronomy.

Written by many of the world's leading experts in the field, The Illustrated Encyclopedia of the Universe combines authority and integrity with real accessibility, covering every aspect of the subject, from the first tentative explanations of Earth's place in the Universe, right through to the latest developments in quantum theory and space technology. Enhanced by hundreds of breathtaking photographs, illustrations, and diagrams, the encyclopedia offers a comprehensive, easy-to-use and visually dramatic book-air essential guide to interested readers of all levels.

 The Illustrated Encyclopedia of the Universe offers a complete understanding of astronomy and space science in one authoritative and accessible volume. Combining all-encompassing information with visual appeal, each thematic chapter highlights the major concepts and developments that have broadened our understanding of the Universe, and brings to life its mystery and magnificence.

Written and edited by many of the world's leading names in astronomy and physics, and with over 900 photographs, illustrations and diagrams, the encyclopedia covers every possible aspect of the subject:

• The earliest views on the Universe and Earth's place in it, through to the latest ideas about how it all began­ and where it might end.
• All the pioneering theories and breakthrough experiments that explain how everything exists in the Universe, from Relativity to Quantum Mechanics.
• Every step of man's exploration of space: the first steps, the Space Race, and today's cutting-edge technology.
• Descriptions and analysis of everything in our Solar System-and what lies beyond.
• Star charts to help the amateur astronomer identify objects in the night sky.
• Thematic entries highlighting milestone events, key people, major concepts and offering practical advice on studying the skies.
• An extensive reference section with complete planetary and stellar data, and details of space missions and craft.

Ideal for background reading, study, or for use as a wide-ranging reference work, The Illustrated Encyclopedia of the Universe will appeal to science buffs, students, amateur astronomers, and family members alike.

The Neptune File: A Story of Astronomical Rivalry and the Pioneers of Planet Hunting by Tom Standage (Walker) chronicles the dramatic events surrounding the discovery of the eighth planet, and the human story of two remarkable men who pioneered the field of planet hunting that is the hottest field in astronomy today.

In 1845, John Couch Adams, a brilliant young mathematician at Cambridge University, theorized that an unseen planet had to exist in a particular spot in the heavens, as this was the only way to explain the erratic orbit of Uranus, which had been discovered almost 70 years earlier. England's Astronomer Royal, George Airy, failed to act on Adams' calculations; this controversial lapse would have international repercussions as a rival French astronomer, Urbain Le Verrier, soon thereafter calculated the planet's position and was credited with the discovery when Neptune was found and named - the first planet discovered by calculation rather than observation. Drawing on long-lost documents in George Airy's Neptune scrapbook, which resurfaced at an observatory in Chile in 1999, The Neptune File is a tale of heroes and cranks, amateur astronomers and knighted celebrities. And it introduces a tale that continues to unfold - since 1995, more than 40 planets have been "discovered" in other solar systems, yet not one of them has actually been seen. Their discovery - and the history of science - owes much to the two men who dared to first place celestial calculation before observation.

Excerpt:

Sometime between ten and eleven o'clock on the night of Tuesday, March 13, 1781, William Herschel was looking at the stars through a homemade telescope from his garden in the English spa town of Bath. Herschel was a musician by trade, but his passion for astronomy had grown over the previous few years to the point that he was spending more time with his astronomical instruments than with his musical ones. What he saw through his telescope that night was to change his life completely and win him widespread and lasting fame. He was about to become the first person to discover a new world.

    For centuries, astronomers had followed the five "classical" planets—Mercury, Venus, Mars, Jupiter, and Saturn—across the skies. The existence of these planets, which resemble bright stars clearly visible to the naked eye, has been known to humankind almost from the beginning of civilization itself. But since antiquity nobody had ever discovered any additional planets, and the idea that there might be more such objects lurking in the heavens seemed outlandish.

    Herschel was in a unique position to make such a fortuitous discovery. Having taught himself astronomy, he had little interest in the tedious business of measuring the positions of the stars or working out tables of the positions of the Moon and planets, which was what professional astronomers spent most of their time doing. Instead, as an amateur, he was free to roam the skies at will, looking at whatever took his fancy. At the same time, Herschel was no ordinary amateur. As a result of the trial-and-error process of learning to build his own telescopes, he had, without realizing it, become the finest telescope maker in the world.

    The telescope he was looking through on that chilly March night was one of his favorites: 7 feet long, 7 inches in diameter, with a wooden tube and a handmade mirror that was the result of hours of painstaking grinding and polishing. The tube was supported by an elaborate wooden frame, with a system of cords and pulleys and three small crank-handles to adjust its position. Herschel also had beside him a set of his own eyepieces, each one mounted in a tube of cocus wood, the kind of wood used in the body of an oboe—one of the first musical instruments he had learned to play as a boy. By removing one eyepiece and inserting another, Herschel could vary the magnifying power of his telescope.

    Increasing the magnification would, for example, make a planet (such as Jupiter or Saturn) appear larger and more distinct. Herschel particularly enjoyed looking at Saturn, which, with its spectacular ring system, is a magnificent sight in even the smallest, feeblest telescope. But on that particular night he was looking at stars, not planets, using one of his less powerful eyepieces, with a magnifying power of 227 times.

    As he swept the telescope over the constellation of Gemini, Herschel noticed something unusual. He decided to take a closer look and removed the telescope's eyepiece in order to substitute a more powerful one. Switching to the eyepiece with a magnification of 460, he found that his mystery object appeared twice as large as it had under a magnification of 227; when he switched to the eyepiece with a magnification of 932, it doubled in size again. Because stars are so distant that they appear as points of light, no matter how great the magnification, this meant the mystery object was definitely not a star. So he noted it in his astronomical journal as "a curious either nebulous star or perhaps a comet."

    The object was essentially a slightly fuzzy blob. Herschel knew that a fuzzy blob could be one of two things: a nebula (a generic term covering all manner of star clouds, clusters, and what we now know are distant galaxies) or a comet (an orbiting snowball within our own solar system that brightens and spews out a tail of gas and dust as it approaches the Sun). The two can be told apart by seeing whether or not they move relative to the fixed stars. Nebulae, like stars, stay fixed; comets, like planets, move from one night to the next. Hoping that perhaps he had discovered a comet, Herschel noted its position so he could observe it after a few days and see if it was still in the same place. A few days later, on the night of Saturday March 17, he noted in his journal, "I looked for the comet or nebulous star, and found that it is a comet, for it has changed its place."

    To have discovered a comet was quite an achievement, and Herschel knew what to do: He had to inform the astronomical community as quickly as possible, to establish his priority as the discoverer. In those days, the members of the worldwide scientific community informed each other of new discoveries, theories, and experiments via a constant blizzard of correspondence, often sending or receiving dozens of letters in a single day. So Herschel, who was only a peripheral member of this informal international network, immediately sent a letter containing the details of his comet to the most senior astronomer he knew: Thomas Hornsby, the director of the observatory in Oxford, with whom he had exchanged a few letters in the past. Through his friend William Watson, who moved in scientific circles in London, Herschel also informed Nevil Maskelyne, at the Royal Greenwich Observatory. Maskelyne was the astronomer royal, the most senior astronomer in the country.

    Maskelyne found the comet almost immediately, and Hornsby found it a few days later. But they both realized that there was something highly unusual about it. "The last three nights I observed stars near the position pointed out by Mr Herschel, whereby I was enabled last night to discern a motion in one of them," Maskelyne wrote to Watson on April 4. But, he added, if this moving star was indeed a comet, it was "very different from any comet I ever read any description of or saw. This seems a comet of a new species." Maskelyne suggested that Herschel write a paper and send it to the Royal Society, the preeminent British scientific society, describing his telescope and his discovery.

    Herschel's comet was unusual because unlike other comets, it had no tail and was not surrounded by a fuzzy cloudlike coma. In fact, it was hardly fuzzy at all. Maskelyne began to suspect that Herschel's comet was, in fact, an entirely new planet.

    Most astronomers were not so sure. Herschel continued to observe what he assumed was a comet, and wrote up his results in a paper that Watson passed to the Royal Society in London, where it was read out loud at the April 26 meeting. Since London was several hours' journey from his home in Bath, Herschel did not attend. Modestly titled "Account of a Comet," his article nonetheless stirred up astonishment and skepticism in equal measure. For although Herschel's account of his discovery was straightforward enough, his casual reference to his eyepieces of 460 and 932 times magnification—along with two others of 1,536 and 2,010 times—astounded the astronomers present. Not even the astronomer royal's telescope, one of the finest available, could magnify any more than 270 times. So Herschel, with his wild claims about the power of his homemade telescope, sounded like a crank.

    Crank or not, there was no denying that Herschel's comet was real and could be seen by any competent astronomer as it made its way through the heavens. Word of the comet soon reached astronomers overseas. Charles Messier, Maskelyne's counterpart in France and a senior figure at the Academy of Sciences (the French equivalent of the Royal Society), wrote to Herschel as soon as he heard of the discovery. A keen comet hunter himself, Messier was particularly impressed by Herschel's ability to spot such a small, faint object.

    As summer approached and the evenings grew lighter, Herschel's comet was lost in the evening twilight and could not be observed again until August. By the time it reappeared in the darkening autumn skies, astronomers had started trying to calculate its orbit.

    To begin with, they based their calculations on the assumption that the orbit was the usual shape for a cometary orbit, a mathematical curve called a parabola. Traveling on a parabolic orbit, a comet swoops in toward the Sun and then hurtles off again into the far reaches of the solar system. But working out a parabolic orbit for Herschel's comet that corresponded to its actual observed motion from night to night proved to be impossible. Even orbits that correctly predicted the comet's motion for a few days quickly became hopelessly inaccurate. Stranger still, the comet did not seem to be getting any larger or brighter, as comets normally do; indeed, Messier noted that with its small disk and whitish light, similar to that of the planet Jupiter, the comet was unlike any of the eighteen comets he had previously observed.

    Anders Lexell, a celebrated mathematician and astronomer from St. Petersburg, Russia, decided to try a different approach. Instead of deriving a parabolic orbit, as would be expected for a comet, he derived the sort of orbit that would be expected of a planet. In 1609 the German astronomer Johannes Kepler had shown that the planets travel around the Sun in almost-circular ellipses. So Lexell performed a calculation to see if the motion of Herschel's comet was consistent with a circular orbit. To his surprise, he found that it was. Furthermore, the orbit was far beyond that of Saturn, the most distant planet from the Sun. Lexell's results, and similar calculations performed soon afterward by other astronomers, tipped the balance of opinion in favor of the idea that Herschel had indeed discovered a planet—one whose faintness, due to its great distance, had prevented anyone from noticing it before.

    This was a truly momentous discovery, and it prompted Sir Joseph Banks, president of the Royal Society, to write to Herschel in November 1781. "Some of our astronomers here incline to the opinion that it is a planet and not a comet," he declared. "If you are of that opinion, it should forthwith be provided with a name." If Herschel failed to move fast, Banks suggested, "our nimble neighbours, the French, will certainly save us the trouble of baptizing it."

    In the same letter Banks also announced that the Council of the Royal Society had decided to award Herschel its highest honor, an annual prize called the Copley Medal, which Herschel was invited to London to receive. At the presentation ceremony on November 30, Sir Joseph made a speech praising Herschel for his discovery of a new planet and for having provided astronomers with a mysterious new body to observe, chart, and scrutinize. He then presented the medal, to great applause.

At the time he made his discovery Herschel was living a double life, combining music with astronomy. His journal entries contain an odd mixture of details of concerts, music lessons, and pupils one minute, and mirrors, glasses, putty, and star maps the next. He was obsessed; every spare moment was devoted to polishing mirrors, building telescopes, and observing the heavens. Often he would return from a concert or a social occasion in Bath and go straight to his telescopes. As his sister Caroline noted in her memoirs, "Every leisure moment was eagerly snatched at for resuming some work which was in progress, without taking time for changing dress, and many a lace ruffle was torn or bespattered by molten pitch."

    Mirror making in particular is not a job for the halfhearted, since the mirror must be continuously polished for hours at a time in order to be free of imperfections. On one occasion, noted Caroline, "by way of keeping him alive I was even obliged to feed him by putting the Vitals by bits into his mouth. This was once the case when at the finishing of a seven-foot mirror. He had not left his hands from it for 16 hours altogether. And in general he was never unemployed at meals, but always at the same time contriving or making drawings of whatever came into his mind. And generally I was obliged to read to him when at some work which required no thinking."

 

On The Revolutions of Heavenly Spheres by Nicolaus Copernicus, Stephen Hawking (On the Shoulders of Giants: Running Press) The Ptolemaic system of the universe, with the earth at the center, had held sway since antiquity as authoritative in philosophy, science, and church teaching. Following his precise observations of the heavenly bodies, Nicolaus Copernicus (1473-1543) abandoned the geocentric system for a heliocentric model, with the sun at the center. His remarkable work, On the Revolutions of Heavenly Spheres, stands as on of the supreme monuments of science. It led to one of the greatest intellectual revolutions of all time, and profoundly influenced, among others, Galileo and Sir Isaac Newton. This essay by Copernicus revolutionized the way we look at the earth's placement in the universe, and paved the way for many great scientists, including Galileo and Isaac Newton, whose theories stemmed from this model. Featuring a biography of Copernicus and an accessible, enlightening introduction, both written by the renowned physicist Stephen Hawking, On the Revolution of Heavenly Spheres provides a fascinating look at the theories which shaped our modern understanding of astronomy and physics.

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