Carl Sagan (1934-1996) was a famous and brilliant astronomer who was also a great speaker and presenter. I was a big fan of Carl Sagan back in the 1980s and learned a lot from Cosmos, we all did. Sagan spoke of complex issues in ways that were easy to understand and made you excited about science. He did not dumb down the issues, he simply had an engaging and unique way of putting the issue in context and illuminating and illustrating his points in a way that listeners could comprehend. He was a scientist-presenter who cared about being clear and about being understood.

When Carl Sagan spoke of statistics he usually followed the number with an illustration or comparison to make it understandable in context. Numbers alone are meaningless. The question is always what do the numbers mean, and compared to what? In the beginning of this clip below you can watch a good example of Sagan doing this without any visuals, though his words create the visuals in your head (which is sometimes even more effective). For example, how much is 20 tons of TNT? Enough for a single bomb to destroy an entire block. All the bombs used in World War II, Sagan says, amounted to two megatons of TNT or the equivalent of a hundred thousand "blockbuster" bombs. So now we can visualize all the explosive, deadly destruction that took place in all of WWII (1939-1945). We can "see" the horrible impact of two megatons of TNT. Two megatons of TNT is now not an abstraction. Then Sagan drops a bomb of his own:

"Today, two megatons is the equivalent of a single thermonuclear bomb—one bomb with the destructive force of the second world war."

 

Perspective
It's always hard to see the forest for the trees. Good presenters will ask us to step back and examine the problem from another perspective to better see what is true and what is not. In the clip above Sagan says:

"How would we explain all this to a dispassionate, extraterrestrial observer? What account would we give of our stewardship of the planet earth?"

By asking us to look at the problem from the point of view of an "extraterrestrial" (i.e., a dispassionate outside observer) then the problem need not be obstructed by abstractions such as nation, political party, religion, etc. Sagan says that "from the extraterrestrial perspective, our global civilization is clearly on the edge of failure and the most important task it faces is preserving the lives and well-being of its citizens and the future habitability of the planet."

Sagan's words here remind us that we as a species are the most remarkably intelligent, creative, and innovative species on the planet, yet paradoxically and incomprehensibly, we also can be, at times, the stupidest. Nonetheless, there is hope. Sagan says there is emerging a new consciousness which sees the earth as a single organism. A consciousness that understands that an organism at war with itself is doomed. We know who speaks for the nations, Sagan says, but who speaks for the earth? The answer, of course, is we do. Though it does not appear in this clip above, this is Sagan's concluding comment:

"Our loyalties are to the species and to the planet. We speak for earth. Our obligation to survive and flourish is owed not just to ourselves but also to that cosmos ancient and vast from which we spring!"

Below is a quote from Carl Sagan's Cosmos that goes very well with this photo of Earth I pointed to earlier.

"Fanatic ethnic or religious or national identifications are a little difficult to support when we see our planet as a fragile, blue crescent fading to become an inconspicuous point of light against the bastion and citadel of the stars."  —Carl Sagan
                                                          
Pale Blue Dot
Below is a slideshow set to Carl Sagan's narration. The message is wonderful and the simple photographic images amplify the message well. I think this is beautiful and puts "it"—our lives, our responsibilities, worries and our dreams—in perspective. It is this distant image of our tiny world—the only one we've got—that underscores, says Sagan, "our responsibility to deal more kindly with one another" and to preserve and cherish our home, the planet Earth.

 

Metaphor
Some of the graphics will seem a bit dated in this clip below, but this clip is a good example of using a metaphor and simple graphics to help illuminate a complex issue. You can argue that it is too simple, but  remember that this kind of calendar metaphor to explain the history of the universe is not meant to be the end of the conversation, it is only meant to be the beginning. We have a choice, says Sagan, but what happens in the first second of the next cosmic year (i.e., now) depends on what we do with our intelligence and knowledge.



Here's the Cosmic Calendar from Discovery Education. Each month represents about one billion years.


December of the "Cosmic Calendar."

NOTE
The same version of this article (with some editing) appeared in the magazine Communicating Astronomy with the Public (CAP) in 2008 (PDF available here). Also available on the The Smithsonian/NASA Astrophysics Data System website here. As we are all getting quite excited to see the new Cosmos with Neil deGrasse Tyson — another great communicator of science —I thought it was worth posting this here.

LINKS
• The International Year of Astronomy 2009 
• Communicating Astronomy with the Public (CAP Journal)