Carl Sagan, renowned astrophysicist and one of the great interpreters of modern science, is largely remembered for his seminal work, the TV series Cosmos: A Personal Voyage, originally broadcast in 1980. The material for the groundbreaking series was also included in a book published the same year. Imagined as a voyage through space and time, Cosmos takes the reader through the history of human evolution and space exploration and examines the possibilities for humanity’s future. The television series and the book tell the expansive story not only of the origins of life on Earth, but also of the birth of comets, planets, and stars. The television series won two Emmys and a Peabody award and is still one of the most widely watched documentary series ever broadcast. The book won the Hugo award for best non-fiction science book. The series was remade as Cosmos: A Spacetime Odyssey in 2014, with Neil DeGrasse Tyson taking the place of host after Sagan’s death in 1996, and followed up by Cosmos: Possible Worlds in 2020. Some of Sagan’s original ideas reflect the biases and limits of his time, yet his remarkable influence cannot be discounted.

All quotations in this guide are derived from the Random House paperback edition published in 1983.

Summary

Carl Sagan’s Cosmos recounts the story of the beginning of the universe—what scientists call the Big Bang—and of the evolution of life on Earth and the possibilities for life elsewhere. Each chapter corresponds to a particular cosmic phenomenon or event, and evocative chapter titles encourage the reader to consider how discoveries and inquiry fuel the future. The author is primarily concerned with the ways in which the universe has been understood and what that means for the progress of humanity.

The Introduction encapsulates the quest to turn scientific innovation into a series for public television. Chapter 1, “The Shores of the Cosmic Ocean,” focuses on the vastness of the cosmos and Earth’s small place in it, noting that the desire to discover other life in the universe is a uniquely human enterprise—at least as far as is known at this point in time. Chapter 2, “One Voice in the Cosmic Fugue,” summarizes how human evolution has shaped life on Earth, as well as how life elsewhere might look, sound, and exist in a totally different manner. This speculation is rooted in what was then the most up-to-date scientific information.

Chapter 3, “The Harmony of the Worlds,” examines the laws of nature, as known on Earth, and introduces the reader to Ptolemy, the ancient Greek scholar who harbored prescient ideas about the makeup of the universe, along with 16th-century astronomers Johannes Kepler and Tycho Brahe. The discovery of elliptical orbits and the later contributions by 18th-century mathematician Isaac Newton about gravity and inertia still inform the study of the planets and galaxies today. Chapter 4, “Heaven and Hell,” reveals that the history of life on Earth—and, thus, of the possibility of life elsewhere—has always been beset by peril and uncertainty. It also advocates that science be allowed to progress freely and without bias in order to determine the nature of Earth and the universe beyond it.

Chapter 5, “Blues for a Red Planet,” explores the relationship between Mars as a cosmic reality and as a cultural artifact. Writers and philosophers throughout history have been fascinated with the so-called Red Planet and the possibilities for life there—whether or not their conjectures have been supported by demonstrable science. Chapter 6, “Travelers’ Tales,” demonstrates that humanity’s thirst for exploration and discovery began many centuries ago. The modern desire for space travel is an extension of this age-old pursuit. Chapter 7, “The Backbone of the Night,” continues the idea that humanity has always been fascinated with the stars—the author is merely following in the footsteps of such celebrated minds as the ancient Greek philosophers Theodoros of Cyrene and Pythagoras, celebrated mathematicians who changed how their contemporaries—and those that followed—understood this world and the cosmos beyond.

In Chapter 8, “Travels in Space and Time,” the author acknowledges the importance of Albert Einstein’s Theory of Relativity and the historic launch of the Voyager spacecraft, designed to explore the universe to its very edges. Chapter 9, “The Lives of the Stars,” explores the connection between all life in the universe—at least that of which is known—and the stuff of stars. Essentially, the same elements make up stars and animate life on Earth. Chapter 10, “The Edge of Forever,” looks at the ways in which space and time, along with other cosmic phenomena, form the fabric of the cosmos.

“The Persistence of Memory,” the title to Chapter 11, speaks to how human civilization evolved to understand science and to record history—not to mention understanding the fact that other animals on Earth also communicate, such as whales. In Chapter 12, “Encyclopaedia Galactica,” the author imagines what contact with another civilization would look like, investigating the recorded human history of exploration and contact as a metaphor for what it might mean to encounter an entirely different race and society from interstellar space.

Finally, Chapter 13, “Who Speaks for Earth?”, is an extended examination of humanity’s place in the cosmos and what our future might hold. Though the author warns of the proliferation of technological weapons of mass destruction, he is largely positive about what the people on Earth can do, given time and knowledge—and peace. He posits that, “The exploration of the Cosmos is a voyage of self-discovery” (318), and in that process of exploration, humanity might find a lasting harmony.

The number of chapters in the book corresponds to the number of episodes in the documentary series, originally aired on public television in 1980. While Sagan claims, as in the subtitle of the series, that this was A Personal Voyage, he also always intended it to be a search for the origins and substance of the cosmos, as well as for the best that humanity has to offer: “Our obligation to survive is owed not just to ourselves but also to that Cosmos, ancient and vast, from which we spring” (345). Thus, the Cosmos awaits that best and earnest effort.