An intelligent person who is not only well-versed in his/her subject, but is also graced with an ability to make that subject come to life for others who may not have as much knowledge. A Sagan knows how to evoke childlike wonder and awe, while not taking himself/herself too seriously. Humanisitic, warmhearted, optimistic, and unpretentious. Not just a sage - a Sagan.
"That Neil DeGrasse Tyson - what an excellent example of a Sagan!"

"Yeah, David Suzuki too!"
by smendler May 22, 2013
A unit of measurement equalling "billions and billions"

From Carl Sagan, well-known astronomer and popular science author
On a clear night, you can see a whole sagan of stars.

Don't drink the water - there's a sagan of germs swimming around in there!
by Serai April 5, 2004
One of the greatest popularizers of science to have walked the Earth.

Carl Sagan achieved worldwide fame for his thirteen-episode series 'Cosmos: A Personal Voyage'.
His research was what brought about the theory of a nuclear winter as the result of nuclear warfare.

Carl Sagan criticized society and advocated skeptical thought. He had strong, yet calm, power in his voice, and with it, the power to pull out a feeling in one's body, a feeling of longing. A yearning to learn, and a desire to venture outside our small planet.

Carl Sagan died in 1996 of pneumonia, but he lives on in any one who has ever listened to him and taken heed of his words.
-What do you think of Carl Sagan?
-He's brilliant.
by Zaborack February 19, 2010
Carl Sagan was(R.I.P) an astronomer who was in awe of the universe, its galaxies, how it all worked, why, what it consists of. The list could go on and on. He was in love with astronomy. Carl sagan had a tv series as well known as the cosmos. Carl made learning about astronomy even MORE interesting, breathtaking, and fun. Carl sagan was a sexy, turtleneck wearing, intelligent, star gazing, time traveling astronomer who made huge leaps in the field of astronomy through teaching, researching, and exploring.
Yeah pete is smart and cute,but he is not for me because he is NO Carl Sagan.
by Andromedamm November 4, 2010
A famous scientist who studies things such as the cosmos. He became famous through his thirteen-episode television show, cosmos: a personal voyage.
I sure like Carl Sagan's narration on the Cosmos show.
by Seshie October 4, 2008
Carl Sagan is a man who studies the cosmos. He is not a priest...
His videos can most commonly be watched in Mr. Kruse's science classroom.
Carl Sagan is a beast. If he wasn't dead I would marry him and we would travel the cosmos together.
by Lorlenks May 25, 2009