Right now cosmic forces prowl the universe and threaten man's very existence. They're asteroids and comets; they've left their imprint on planet Earth, literally. Initially helping to build planets through violent collisions, during this fiery bombardment period they may have even seeded Earth with water and the building blocks for life. Since the turbulent formation of the solar system, these space rocks have continued to impact Earth. Some have been so violent that they've led to mass extinctions, including one that wiped out the dinosaur. New theories suggest that asteroid and comet dust harbour deadly viruses that may have triggered some of our worst pandemics. The possibility of future collisions remains a legitimate threat yet despite their dangers, asteroids and comets may hold vital natural resources, which could actually preserve

Take a tour through the Art Gallery of the Galaxy and view what are considered the "crown jewels" of the heavens. Nebulas are mysterious clouds of gas that aren't classified as stars, planets, moons or asteroids. Astronomers use the most sophisticated techniques to view them since they are practically invisible to the naked eye. Nothing less than stunning, nebulas glow, reflect or obscure the galaxy's light with amazing swirls of color. Nebulas mark the regions where the nothingness of space first coalesces, where stars are born and where stars die. Cutting-edge computer graphics are used to bring the universe down to earth.

Americans define themselves in the superlative: we are the biggest, strongest, fastest country in the world. They reward above all else: winning – at sport, at business and at war. Metaphorically is a nation on steroids. Is it any wonder that so many of their heroes are on performance enhancing drugs? A film that unflinchingly explores our win-at-all-cost culture. Bigger, Stronger, Faster is a first-person narrative, including US Congressmen, professional athletes, medical experts and everyday gym rats. When you discover that your heroes have all broken the rules, do you follow the rules, or do you follow your heroes?

Find out what is being done to prevent the end of the world from threats from outer space such as comets and asteroids. Also discussed are apocalyptic scenarios.

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.