Carl Sagan was an American astronomer, astrophysicist, and science communicator renowned for his work in popularizing science. His book "Cosmos" and the television series of the same name brought the wonders of the universe to millions of viewers. Sagan's research in planetary science and his advocacy for space exploration and scientific skepticism have made him a prominent and influential figure in science.

"Avoidable human misery is more often caused not so much by stupidity as by ignorance, particularly our ignorance about ourselves."

"Lashley also reported no apparent change in the general behavior of a rat when significant fractions-say 10 percent-of its brain were removed. But no one asked the rat of its opinion."

"Significant change might require those who are now high in the hierarchy to move downward many steps. This seems to them undesirable and is resisted."

"The reappearance of the crescent moon after the new moon; the return of the Sun after a total eclipse, the rising of the Sun in the morning after its troublesome absence at night were noted by people around the world; these phenomena spoke to our ancestors of the possibility of surviving death. Up there in the skies was also a metaphor of immortality."

"The time scale for evolutionary or genetic change is very long. A characteristic period for the emergence of one advanced species from another is perhaps a hundred thousand years; and very often the difference in behavior between closely relatedspecies-say, lions and tigers-do not seem very great... But today we do not have ten million years to wait for the next advance. We live in a time when our world is changing at an unprecedented rate. While the changes are largely of our own making, they cannot be ignored. We must adjust and adapt andcontrol, or we perish."

"These days there seems to be nowhere left to explore, at least on the land area of the Earth. Victims of their very success, the explorers now pretty much stay home."

"The others would then fall silent and she would continue about doped gallium arsenide detectors, or the ethanol content of the galactic cloud W-3. The quantity of 200-proof alcohol in this single interstellar cloud was more than enough to maintain the present population of the Earth, if every adult were a dedicated alcoholic, for the age of the solar system. The tamada had appreciated the remark."

"In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion."

"Often, superstition and injustice are imposed by the same ecclesiastical and secular authorities, working hand in glove. It is no surprise that political revolutions, scepticism about religion, and the rise of science might go together."

"Perhaps the locale of the subjunctive mood willone day be found. Will Latins turn out to be extravagantly endowed and English-speaking peoples significantly short-changed in this minor piece of brain anatomy?"

"The idea that God is an oversized white male with a flowing beard, who sits in the sky and tallies the fall of every sparrow is ludicrous. But if by 'God,' one means the set of physical laws that govern the universe, then clearly there is such a God. This God is emotionally unsatisfying... it does not make much sense to pray to the law of gravity."

"Does trying to understand the universe at all betray a lack of humility? I believe it is true that humility is the only just response in a confrontation with the universe, but not a humility that prevents us from seeking the nature of the universe we are admiring. If we seek that nature, then love can be informed by truth instead of being based on ignorance or self-deception. If a Creator God exists, would He or She or It or whatever the appropriate pronoun is, prefer a kind of sodden blockhead who worships while understanding nothing? Or would He prefer His votaries to admire the real universe in all its intricacy? I would suggest that science is, at least in part, informed worship."

"It goes with a courageous intent to greet the universe as it really is, not to foist our emotional predispositions on it but to courageously accept what our explorations tell us."

"Major scientific insights are characteristically intuitive, and equally characteristically described in scientific papers by linear analytical arguments. There is no anomaly in this: it is, rather, just as it should be. The creative act has major right-hemisphere components. But arguments on thevalidity of the result are largely left-hemisphere functions."

"With rare exceptions (chiefly the social insects), mammals and birds are the only organisms to devote substantial attention to the care of their young; an evolutionary development that, through the long period of plasticity which it permits, takes advantage of the large information-processing capability of the mammalian and primate brains. Love seems to be an invention of the mammals."

"For their surface area, insects weigh very little. A beetle, falling from a high altitude, quickly achieves terminal velocity: air resistance prevents it from falling very fast, and, after alighting on the ground, it will walk away, apparently none the worse for the experience. In contrast, human beings are characteristically maimed or killed by any fall of more than a few dozen feet: because of our size, we weigh too much for our surface area."

"There is a reward structure in science that is very interesting: Our highest honors go to those who disprove the findings of the most revered among us. So Einstein is revered not just because he made so many fundamental contributions to science, but because he found an imperfection in the fundamental contribution of Isaac Newton."

"What functions do dreams serve today? One view, published in a reputable scientific paper, holds that the function of dreams is to wake us up a little, every now and then, to see if anyone is about to eat us. But dreams occupy such a relatively small part of normal sleep that this explanation does not seem very compelling. Moreover, as we have seen, the evidence points just the other way: today it is the mammalian predators, not the mammalian prey, who characteristically have dream-filled sleep."

"It is the responsibility of scientists never to suppress knowledge, no matter how awkward that knowledge is, no matter how it may bother those in power; we are not smart enough to decide which pieces of knowledge are permissible, and which are not."

"Natural selection has served as a kind of intellectual sieve, producing brains and intelligences increasingly competent to deal with the laws of nature."

"One glance at (a book) and you hear the voice of another person - perhaps someone dead for thousands of years. Across the millenia, the author is speaking, clearly and silently, inside your head, directly to you. Writing is perhaps the greatest of human inventions, binding together people, citizens of distant epochs, who never knew one another. Books break the shackles of time."

"The significance of our lives and our fragile planet is then determined only by our own wisdom and courage. We are the custodians of life's meaning. We long for a Parent to care for us, to forgive us our errors, to save us from our childish mistakes. But knowledge is preferable to ignorance. Better by far to embrace the hard truth than a reassuring fable. If we crave some cosmic purpose, then let us find ourselves a worthy goal."

"Perhaps the most striking aspect of this entire subject is that there are nonhuman primates so close to the edge of language, so willing to learn, so entirely competent in its use and inventive in its application once the language is taught. But this raises a curious question: Why are they all on the edge? Why are there no nonhuman primates with an existing complex gestural language? One possible answer, it seems to me, is that humans have systematically exterminated those other primates who displayed signs of intelligence."

"Why do we put up with it? Do we like to be criticized? No, no scientist enjoys it. Every scientist feels a proprietary affection for his or her ideas and findings. Even so, you don't reply to critics, Wait a minute; this is a really good idea; I'm very fond of it; it's done you no harm; please leave it alone. Instead, the hard but just rule is that if the ideas don't work, you must throw them away."

"The vast distances that separate the stars are providential. Beings and worlds are quarantined from one another. The quarantine is lifted only for those with sufficient self-knowledge and judgment to have safely traveled from star to star."

"There are no forbidden questions in science, no matters too sensitive or delicate to be probed, no sacred truths."

"The price we pay for the anticipation of our future is anxiety about it."

"A new concept of god: "something not very different from the sum total of the physical laws of the universe; that is, gravitation plus quantum mechanics plus grand unified field theories plus a few other things equaled god. And by that all they meant was that here were a set of exquisitely powerful physical principles that seemed to explain a great deal that was otherwise inexplicable about the universe. Laws of nature that apply not just locally, not just in Glasgow, but far beyond: Edinburgh, Moscow, Mars, the center of the Milky Way, and out by the most distant quarters known. That the same laws of physics apply everywhere is quite remarkable. Certainly that represents a power greater than any of us."

"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."

"What do you do when you are faced with several different gods each claiming the same territory? The Babylonian Marduk and the Greek Zeus was each considered master of the sky and king of gods. You might also decide, since they had quite different attributes, that one of them was merely invented by the priests. But if one, why not both? And so it was that the great idea arose, the realization that there might be a way to know the world without the god hypothesis; that there might be principles, forces, laws of nature, through which the world could be understood without attributing the fall of every sparrow to the direct intervention of Zeus."

"In college, in the early 1950s, I began to learn a little about how science works, the secrets of its great success, how rigorous the standards of evidence must be if we are really to know something is true, how many false starts and dead ends have plagued human thinking, how our biases can colour our interpretation of evidence, and how often belief systems widely held and supported by the political, religious and academic hierarchies turn out to be not just slightly in error, but grotesquely wrong."

"We will know which stars to visit. Our descendants will then skim the light years, the children of Thales and Aristarchus, Leonardo and Einstein."

"Those at too great a distance may, I am well are, mistake ignorance for perspective."

"Science cuts two ways, of course; its products can be used for both good and evil. But there's no turning back from science. The early warnings about technological dangers also come from science."

"The prediction I can make with the highest confidence is that the most amazing discoveries will be the ones we are not today wise enough to foresee."

"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 far the best tool we have, self-correcting, ongoing, applicable to everything."

"I would expect a significant development and elaboration of language in only a few generations if all the chimps unable to communicate were to die or fail to reproduce. Basic English corresponds to about 1,000 words. Chimpanzees are already accomplished in vocabularies exceeding 10 percent of that number."

"The major religions on the Earth contradict each other left and right. You can't all be correct. And what if all of you are wrong? It's a possibility, you know. You must care about the truth, right? Well, the way to winnow through all the differing contentions is to be skeptical. I'm not any more skeptical about your religious beliefs than I am about every new scientific idea I hear about. But in my line of work, they're called hypotheses, not inspiration and not revelation."

"If we can't think for ourselves, if we're unwilling to question authority, then we're just putty in the hands of those in power. But if the citizens are educated and form their own opinions, then those in power work for us. In every country, we should be teaching our children the scientific method and the reasons for a Bill of Rights. With it comes a certain decency, humility and community spirit. In the demon-haunted world that we inhabit by virtue of being human, this may be all that stands between us and the enveloping darkness."