Dr. Carl Sagan worked as an author, astronomer and teacher. Started out at Harvard and then went on to the Smithsonian Observatory and then finally in 1970 to Cornell University as a professor of astronomy and space sciences.
Before spending most of his time giving lectures, writing or promoting books or appearing on TV, he made important contributions to the study of the atmospheres of our solar system. He was the first to explain the high surface temperature of Venus as an result of the greenhouse effect. He also contributed to the studies of the origins of life and the importance of the atmospheric environment.
He was also involved in most projects of sending unmanned spacecraft for space exploration; Mariner, Pioneer, Voyager, Viking and Galileo. He was a strong advocate for SETI and helped collect a lot of money for different SETI research projects. At Cornell he created a new field of science, exobiology, dedicated to the study of alien life forms.
Carl Sagan wrote and co-wrote many books on various aspects of science, see below, and he also hosted the world famous and acclaimed TV-series Cosmos.
Most of all, he was a teacher for all of us physics and astronomy junkies.
Dr. Carl Sagan died of a bone marrow disease in 1996.
Bibliography
Can we know, ultimately, and in detail, a grain of salt? Consider one microgram of table salt, a speck just barely large enough for someone with keen eyesight to make out without a microscope. In that grain of salt there are about 1016 sodium and chlorine atoms. . . . If we wish to know a grain of salt, we must at least know the three-dimensional positions of each of these atoms. (In fact, there is much more to be known -- for example, the nature of the forces between the atoms -- but we are making only a modest calculation.) Now, is this number more or less than the number of things the brain can know? How much can the brain know? There are perhaps 1011 neurons in the brain, the circuit elements and switches that are responsible for the functioning of our minds. A typical brain neuron has perhaps a thousand little wires, called dendrites, which connect it with its fellows. If, as seems likely, every bit of information in the brain corresponds to one of these connections, the total number of things knowable by the brain is no more than 1014, one hundred trillion. But this number is only one percent of the number of atoms in our speck of salt. But let us look a little more deeply at our microgram of salt. Salt happens to be a crystal in which, except for defects in the structure of the crystal lattice, the position of every sodium and chlorine atom is predetermined. . . . An absolutely pure crystal of salt could have the position of every atom specified by something like 10 bits of information. This would not strain the information-carrying capacity of the brain. If the universe had natural laws that governed its behavior to the same degree of regularity that determines a crystal of salt, then, of course, the universe would be knowable. from Broca's Brain
"Let's see if I've got this straight," he returned. . . . "It's a lazy Sunday afternoon, and there's this couple lying naked in bed reading the Encyclopedia Britannica to each other, arguing about whether the Andromeda Galaxy is more 'numinous' than the Resurrection. Do they know how to have a good time, or don't they?" from Contact
"A fire-breathing dragon lives in my garage." . . . "Show me," you say. I lead you to my garage. You look inside and see a ladder, empty paint cans, an old tricycle -- but no dragon. "Where's the dragon?" you ask. "Oh, she's right here," I reply, waving vaguely. "I neglected to mention that she's an invisible dragon." You propose spreading flour on the floor of the garage to capture the dragon's footprints. "Good idea," I say, "but this dragon floats in the air." Then you'll use an infrared sensor to detect the invisible fire. "Good idea, but the invisible fire is also heatless." You'll spray-paint the dragon and make her visible. "Good idea, except she's an incorporeal dragon and the paint won't stick." . . . Now, what's the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all? . . . The only thing you've really learned from my insistence that there's a dragon in my garage is that something funny is going on inside my head. from The Demon-Haunted World
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