We can't compare anything on earth to the biggest things known in space. The Cosmic Web may connect objects in the universe with threads of Dark Matter. The Lyman-alpha blob is a bubble like structure containing countless galaxies--perhaps the biggest object in the entire universe. Regions of radio-emitting gas called "radio lobes" could be even bigger. Then there are super galaxy clusters which are hundreds of galaxies merged together due to cosmic collisions. Discover which is the largest planet, star, star cluster, constellation, black hole, volcano, galaxy, explosions, moon, storm, impact crater and "void" in space.

Gravity is the most powerful and exacting force in the universe. It is pervasive and penetrating. Gravity binds us together, its reach hangs stars in the sky and its grip crushes light. Gravity holds planets together, and leashes them to their suns. Without gravity, stars, comets, moons, nebulae, and even the Earth itself would not exist. Explore how science and humanity discovered, overcame and utilized gravity. Learn what it takes to propel objects into the heavens, to ride a wave or to ski down a slope. Take a front row seat as an astronaut subjects himself to the weightless wonders of the specially modified aircraft used to train astronauts known as the "Vomit Comet."

Low Earth Orbit, 120 miles above sea level, is where the majority of space exploration has occurred. This 1,100 mile band around Earth is where--for a cool $20 million--any private citizen can take the vacation of his or her life on the International Space Station. Commercial prospects for LEO are huge; but dangers lurk for any individual willing to travel here--radiation, cosmic rays, and space debris numbering in the thousands threaten any spacecraft travelling in orbit. It's the new frontier, or the final frontier...and the possibilities are endless if you are willing to travel to the edge of space exploration.

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).

Sagan discusses comets and asteroids as planetary impactors, giving recent examples of the Tunguska event and a lunar impact described by Canterbury monks in 1178. It moves to a description of the environment of Venus, from the previous fantastic theories of people such as Immanuel Velikovsky to the information gained by the Venera landers and its implications for Earth's greenhouse effect. The Cosmos Update highlights the connection to global warming.

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.