The surface of the Earth is the shore of the cosmic ocean. On this shore we have learned most of what we know. Recently, we’ve waded a little way out—maybe ankle-deep—and the water seems inviting. Some part of our being knows this is where we came from. We long to return. And we can. Because the cosmos is also within us. We’re made of star-stuff. We are a way for the cosmos to know itself.
Astronomy is the study of celestial objects and phenomena that exist beyond Earth’s atmosphere. For thousands of years, humans have studied the stars and planets visible to the naked eye. Ancient civilizations used observations of celestial bodies to develop calendars, plan agricultural activities, and navigate across oceans. Today, astronomers use ground and space-based telescopes to study electromagnetic radiation from objects many light years away.
Modern astronomy seeks to understand the physics and chemistry behind planetary formation and evolution. Astronomers also study the birth, life, and death of stars. The study of galaxies, galactic clusters, and larger scale cosmic structures falls under the umbrella of extragalactic astronomy. Another branch of modern astronomy is physical cosmology—the study of the universe as a whole, including its structure, origin, and evolution. Astronomy continues to fascinate humans as we uncover mysteries about dark matter, dark energy, black holes, exoplanets, and the incredible scale of our ever-expanding universe that contains billions of galaxies like our own.
The Shores of the Cosmic Ocean
Cosmos, Episode 1
Carl Sagan opens the program with a description of the cosmos and a “spaceship of the imagination” shaped like a dandelion seed. The ship journeys through the universe’s hundred billion galaxies, the Local Group, the Andromeda galaxy, the Milky Way, the Orion Nebula, our solar system, and finally the planet Earth. Eratosthenes’ successful calculation of the circumference of Earth leads to a description of the ancient Library of Alexandria. Finally, the “Ages of Science” are described, before pulling back to the full span of the cosmic calendar.
Harmony of the Worlds
Cosmos, Episode 3
Beginning with the separation of the fuzzy thinking and pious fraud of astrology from the careful observations of astronomy, Sagan follows the development of astronomical observation. Beginning with constellations and ceremonial calendars (such as those of the Anasazi), the story moves to the debate between Earth and Sun-centered models: Ptolemy and the geocentric worldview, Copernicus' theory, the data-gathering of Tycho Brahe, and the achievements of Johannes Kepler (Kepler's laws of planetary motion and the first science-fiction novel).
Travellers' Tales
Cosmos, Episode 6
The journeys of the Voyager probes is put in the context of the Netherlands in the seventeenth century, with a centuries-long tradition of sailing ship explorers, and its contemporary thinkers (such as Constantijn Huygens and his son Christiaan). Their discoveries are compared to the Voyager probes' discoveries among the Jovian and Saturn systems. In Cosmos Update, image processing reconstructs Voyager’s worlds and Voyager’s last portrait of the Solar System as it leaves is shown.
The Lives of the Stars
Cosmos, Episode 9
The simple act of making an apple pie is extrapolated into the atoms and subatomic particles (electrons, protons, and neutrons) necessary. Many of the ingredients necessary are formed of chemical elements formed in the life and deaths of stars (such as our own Sun), resulting in massive red giants and supernovae or collapsing into white dwarfs, neutron stars, pulsars, and even black holes. These produce all sorts of phenomena, such as radioactivity, cosmic rays, and even the curving of spacetime by gravity. Cosmos Update mentions the supernova SN 1987A and neutrino astronomy.
The Edge of Forever
Cosmos, Episode 10
Beginning with the origins of the universe in the Big Bang, Sagan describes the formation of different types of galaxies and anomalies such as galactic collisions and quasars. The episode moves further into ideas about the structure of the Universe, such as different dimensions (in the imaginary Flatland and four-dimensional hypercubes), an infinite vs. a finite universe, and the idea of an oscillating Universe (similar to that in Hindu cosmology). The search into other ideas such as dark matter and the multiverse is shown, using tools such as the Very Large Array in New Mexico. Cosmos Update shows new information about the odd, irregular surfaces of galaxies and the Milky Way perhaps being a barred spiral galaxy.
Encyclopædia Galactica
Cosmos, Episode 12
Questions are raised about the search for intelligent life beyond the Earth, with UFOs and other close encounters refuted in favor of communications through SETI and radio telescope such as the Arecibo Observatory. The probability of technically advanced civilizations existing elsewhere in the Milky Way is interpreted using the Drake equation and a future hypothetical Encyclopedia Galactica is discussed as a repository of information about other worlds in the galaxy. The Cosmos Update notes that there have been fewer sightings of UFOs and more stories of abductions, while mentioning the META scanning the skies for signals.
Who Speaks for Earth?
Cosmos, Episode 13
Sagan reflects on the future of humanity and the question of "who speaks for Earth?" when meeting extraterrestrials. He discusses the very different meetings of the Tlingit people and explorer Jean-Francois de La Perouse with the destruction of the Aztecs by Spanish conquistadors, the looming threat of nuclear warfare, and the threats shown by destruction of the Library of Alexandria and the murder of Hypatia. The episode ends with an overview of the beginning of the universe, the evolution of life, and the accomplishments of humanity and makes a plea to mankind to cherish life and continue its journey in the cosmos. The Cosmos Update notes the preliminary reconnaissance of planets with spacecraft, the fall of the Berlin Wall and the end of apartheid in South Africa, and measures towards the reduction of nuclear weapons.
