Quotes in italics appear in the book, but are attributed to someone other than the author.

"The time will come when diligent research over long periods will bring to light things which now lie hidden. A single lifetime, even thought entirely devoted to the sky, would not be enough for the investigation of so vast a subject... And so this knowledge will be unfolded only through long successive ages. There will be a time when our descendants be amazed that we did not know things that are so plain to them... Many discoveries are reserved for ages still to come, when memory of us will have been effaced. Our universe is a sorry little affair unless it has in it something for every age to investigate... Nature does not reveal her mysteries once and for all." —Seneca (xxi)

"The known is finite, the unknown is infinite; intellectually we stand on an islet in the midst of an illimitable ocean of inexplicability. Our business in every generation is to reclaim a little more land." —T.H. Huxley (1)

"Probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed... There is grandeur in this view of life... that, whilst this planet has gone cycling according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved." —Charles Darwin (17)

"We are like butterflies who flutter for a day and think it is forever." (27)

"We do not ask for what useful purpose the birds do sing, for song is their pleasure since they were created for singing. Similarly, we ought not to ask why the human mind troubles to fathom the secrets of the heavens... the diversity of phenomena of Nature is so great, and the treasures hidden in the heavens so rich, precisely in order that the human mind shall never be lacking in fresh nourishment." —Johannes Kepler (41)

"If we lived on a planet where nothing ever changed, there would be little to do. There would be nothing to figure out. There would be no impetus for science. And if we lived in an unpredictable world, where things changed in random or very complex ways, we would not be able to figure things out. Again, there would be no such thing as science. But we live in an in-between universe, where things change, but according to patterns, rules, or, as we call them, laws of nature." (41)

"I do not know what I may appear to the world; but to myself I seem to have been only like a boy, playing on the seashore, and diverting myself, in now and then finding a smoother pebble or a prettier shell than ordinary, while the great ocean of truth lay all undiscovered before me." —Isaac Newton (75)

"The doors of heaven and hell are adjacent and identical." —Nikos Kazantzakis (76)

"Many hypotheses proposed by scientists as well as by non-scientists turn out to be wrong. But science is a self-correcting enterprise. To be accepted, all new ideas must survive rigorous standards of evidence.... Science is generated by and devoted to free inquiry; the idea that any hypothesis, no matter how strange, deserves to be considered in its merits. The suppression of uncomfortable ideas may be commonplace in religion and politics, but it is not the path to knowledge; it has no place in the endeavor of science. We do not know in advance who will discover fundamental new insights." (94)

"Our intelligence and our technology have given us the power to affect the climate. How will we use this power? Are we willing to tolerate ignorance and complacency in matters that affect the entire human family? Do we value short-term advantages above the health of the earth? Or will we think on longer time scales, with concern for our children and grandchildren, to understand and protect the complex life-support systems of out planet? The earth is tiny and fragile world. It needs to be cherished." (107)

"I am a collection of water, calcium, and organic molecules called Carl Sagan. You are a collection of almost identical molecules with a different collective label. But is that all? Is there nothing in here but molecules? Some people find this idea somehow demeaning to human dignity. For myself, I find it elevating that our universe permits the evolution of molecular machines as intricate and subtle as we." (134)

"The world is my country, science my religion." —Christiaan Huygens (149)

"I would rather understand one cause than be King of Persia." —Democritus of Abdera (171)

"If a faithful account was rendered of Man's ideas upon Divinity, he would be obliged to acknowledge, that for the most part the word "gods" has been used to express the concealed, remote, unknown causes of the natural, the source of known causes, ceases to be visible: as soon as his mind can no longer follow the chain, he solves the difficulty, terminates his research, by ascribing it to his gods... when, therefore, he ascribes to his gods the production of some phenomenon... does he, in fact, do any thing more than substitute for the darkness of his own mind, a sound to which he has been accustomed to listen with reverential awe?" —Paul Heinrich Dietrich, Baron von Holbach (171)

"As a person, Democritus seems to have been somewhat unusual. Women, children, and sex discomfited him, in part because they took away time from thinking. But he valued friendship, held cheerfulness to be the goal of life and devoted a major philosophical inquiry to the origin and nature of enthusiasm. He journeyed to Athens to visit Socrates and then found himself too shy to introduce himself. He was a close friend of Hippocrates. He was awed by the beauty and elegance of the natural world. He felt that poverty in a democracy was preferable to wealth in a tyranny. He believed that the prevailing religions of his time were evil and that neither immortal souls nor immortal gods exist: 'Nothing exists, but atoms and the void.'" (189-190)

"Without experiment, there is no way to choose among contending hypotheses, no way for science to advance." (197)

"A major problem in the contemporary (political) Third World is that the educated classes tend to be the children of the wealthy, with a vested interest in the status quo, and are unaccustomed either to working with their hands or to challenging conventional wisdom." (198-199)

"As long as there have been humans, we have searched for our place in the Cosmos. In the childhood of our species (when our ancestors gazed a little idly at the stars), among the Ionian scientists of ancient Greece, and in our own age, we have been transfixed by this question: Where are we? Who are we? We find that we live on an insignificant planet of a humdrum star lost between two spiral arms in the outskirts of a galaxy which is a member of a sparse cluster of galaxies, tucked away in some forgotten corner of a universe in which there are far more galaxies than people. This perspective is a courageous continuation of our penchant for constructing and testing mental models of the skies; the Sun as a red-hot stone, the stars a celestial flame, the Galaxy as the back-bone of night. There are those who secretly deplore these great discoveries, who consider every step a demotion, who in their heart of hearts still pine for a universe whose center, focus and fulcrum is the Earth. But if we are to deal with the Cosmos we must first understand it, even if our hopes for some unearned preferential status are, in the process, contravened. Understanding where we live is an essential precondition for improving the neighborhood. Knowing what other neighborhoods are like also helps. If we long for our planet to be important, there is something we can do about it. We can make our world significant by the courage of our questions and the depths of our answers." (205)

"We embarked on our cosmic voyage with a question first framed in the childhood of our species and in each generation asked anew with undiminished wonder: What are the stars? Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars." (206)

"If you wish to make an apple pie from scratch, you must first invent the universe." (230)

"The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff." (244)

"It is said that men may not be the dreams of the gods, but rather that the gods are the dreams of men." (273)

"Knowing a great deal is not the same thing as being smart; intelligence is not information alone but also judgement, the manner in which the information is coordinated and used." (285)

"We are the only species on the planet, so far as we know, to have invented a communal memory stored neither in our genes nor in our brains. The warehouse of that memory is called the library.

A book is made from a tree. It is an assemblage of flat, flexible parts (still called "leaves") imprinted with dark pigmented squiggles. One glance at it and you hear the voice of another person— perhaps someone dead for thousands of years. Across the millennia, the author is speaking, clearly and silently, inside your head, directly to you. Writing is perhaps the greatest of human inventions, binding people together, citizens of distant epochs, who never knew one another. Books break the shackles of time, proof that humans work magic." (295-296)

"The library connects us with the insights and knowledge, painfully extracted from Nature, of the greatest minds that ever were, with the best teachers, drawn from the entire planet and from all of our history, to instruct us without tiring, and to inspire us to make our own contributions to the collective knowledge of the human species. Public libraries depend on voluntary contribution. I think the health of our civilization, the depth of our awareness about the underpinnings of our culture and our and our concern for the future can all be tested by how well we support our libraries." (297)

"Our intelligence has recently provided us with awesome powers. It is not yet clear that we have the wisdom to avoid our own self-destruction. But many of us are trying very hard. We hope that very soon in the perspective of cosmic time we will have unified our planet peacefully into an organization cherishing the life of every living creature on it and will be ready to take that next great step, to become part of a galactic society of communicating civilizations." (306)

"How vast those Orbs must be, and how inconsiderable this Earth, the Theatre upon which all our mighty Designs, all our Navigations, and all our Wars are transacted, is when compared to them. A very fit consideration, and matter of Reflection, for those Kings and Princes who sacrifice the Lives of so many People, only to flatter their Ambition in being Masters of some pitiful corner of this small Spot." —Christiaan Huygens (336)

"National boundaries are not evident when we view the Earth from space. Fanatical ethnic or religious or national chauvinisms are a little difficult to maintain when we see our planet as a fragile blue crescent fading to become an inconspicuous pint of light against the bastion and citadel of the stars." (338)

"If we are willing to contemplate a wholesale destruction of our emerging global society, should we not also be willing to contemplate a wholesale restructuring of our societies? From an extraterrestrial perspective, our global civilization is clearly on the edge of failure in the most important task it faces: to preserve the lives and well-being of the citizens of the planet. Should we not then be willing to explore vigorously, in every nation, major changes in the traditional ways of doing things, a fundamental redesign of economic, political, social and religious institutions?" (348)

"If the inclinations towards slavery and racism, misogyny and violence are connected— as individual character and human history, as well as cross-cultural studies suggest— then there is room for optimism. We are surrounded by recent fundamental changes in society. In the last two centuries, abject slavery, with us for thousands of years or more, has been almost eliminated in a planet-wide revolution. Women, patronized for millennia, traditionally denied real political and economic power, are gradually becoming, even in the most backward societies, equal partners with men. For the first time in modern history, major wars of aggression were stopped partly because of the revulsion felt by citizens of the aggressor nations. The old exhortations to nationalist fervor and jingoist pride have begun to lose their appeal. Perhaps because of rising standards of living, children are being treated better worldwide. In only a few decades, sweeping global changes have begun to move in precisely the directions needed for human survival. A new consciousness is developing which recognizes that we are one species." (351)

"Those afraid of the universe as it really is, those who pretend to nonexistent knowledge and envision a Cosmos centered on human beings will prefer the fleeting comforts of superstition. They avoid rather than confront the world. But those with the courage to explore the weave and structure of the Cosmos, even where it differs profoundly from their wishes and prejudices, will penetrate its deepest mysteries." (352)

"There is no other species on Earth that does science. It is, so far, entirely a human invention, evolved by natural selection in the cerebral cortex for one simple reason: it works. It is not perfect. It can be misused. It is only a tool. But it is by for the best tool we have, self-correcting, ongoing, applicable to everything." (352)

"Alexandria was the greatest city the Western world had ever seen. People of all nations came there to live, to trade, to learn. On any given day, its harbors were thronged with merchants, scholars, and tourists. This was city where Greeks, Egyptians, Arabs, Syrians, Hebrews, Persians, Nubians, Phoenicians, Italians, Gauls and Iberians exchanged merchandise and ideas. It is probably here that the word cosmopolitan realized its true meaning— citizen, not just of a nation, but of the Cosmos." (354)

"Here clearly were the seeds of the modern world. What prevented them from taking root and flourishing? Why instead did the West slumber through a thousand years of darkness until Columbus and Copernicus and their contemporaries rediscovered the work done in Alexandria? I cannot give you a simple answer. But I do know this: there is no record, in the entire history of the Library [of Alexandria], that any of its illustrious scientists and scholars ever seriously challenged the political, economic and religious assumptions of their society . The permanence of the stars was questioned; the justice of slavery was not . Science and learning in general were the preserve of a privileged few. The vast population of the city had not the vaguest notion of the great discoveries taking place within the Library. New findings were not explained or popularized. The research benefitted them little. Discoveries in mechanics and steam technology were applied mainly to the perfection of weapons, the encouragement of superstition, the amusement of kings. The scientists never grasped the potential of machines to free people. The great intellectual achievements of antiquity had few immediate practical applications. Science never captured the imagination of the multitude. There was no counterbalance to stagnation, to pessimism, to the most abject surrenders to mysticism. When, at long last, the mob came to burn the Library down, there was nobody to stop them." (354-355)

"There are a million threads from the past intertwined to make the ropes and cables of the modern world." (358)

"Through technological advances in communication our planet is in the final stages of being bound up at a breakneck pace into a single global society. If we can accomplish the integration of the Earth without obliterating cultural differences or destroying ourselves, we will have accomplished a great thing." (358)

"We have held the peculiar notion that a person or society that is a little different from us, whoever we are, is somehow strange or bizarre, to be distrusted or loathed. Think of the negative connotations of words like alien or outlandish. And yet the monuments and cultures of each of our civilizations merely represent different ways of being human. An extraterrestrial visitor, looking at the differences among human beings and their societies, would find those differences trivial compared to the similarities. The Cosmos may be so densely populated with intelligent beings. But the Darwinian lesson is clear: There will be no humans elsewhere. Only here. Only on this small planet. We are a rare as well as an endangered species. Every one of us is, in the cosmic perspective, precious. If a human disagrees with you, let him live. In a hundred billion galaxies, you will not find another." (361)

"If we are to survive, our loyalties must be broadened further, to include the whole human community, the entire planet Earth. Many of those who run the nations will find this idea unpleasant. They will fear the loss of power. We will hear much about treason and disloyalty. Rich nation-states will have to share their wealth with poor ones. But the choice, as H. G. Wells once said in a different context, is clearly the universe or nothing." (362)

"It is almost impossible to maintain a static society. There is a kind of psychological compound interest: even a small tendency toward retrenchment, a turning away from the Cosmos, adds up over many generations to a significant decline. And conversely, even a slight commitment to ventures beyond the Earth— to what we might call, after Columbus, "the enterprise of the stars"— builds over many generations to a significant human presence on other worlds, a rejoicing of our participation in the Cosmos." (364)

"It is almost impossible to maintain a static society. There is a kind of psychological compound interest: even a small tendency toward retrenchment, a turning away from the Cosmos, adds up over many generations to a significant decline. And conversely, even a slight commitment to ventures beyond the Earth— to what we might call, after Columbus, "the enterprise of the stars"— builds over many generations to a significant human presence on other worlds, a rejoicing of our participation in the Cosmos." (364-365)