The famous scientist and popularizer of science poses in his Cornell lab circa 1974, turtleneck sweater and all.

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Resting on the foreign, reddish surface of Mars, a compartment in NASA's Phoenix spacecraft carries a heartfelt message from one of the world's most fascinating researchers. It reads:

"Whatever the reason you're on Mars, I'm glad you're here, and I wish I was with you."

Crafting that message, one of a collection of DVD dispatches intended for future Mars settlers, was just another day for Carl Sagan. Did anyone delight in describing the universe, with its billions of galaxies, as much as Sagan? Who else would launch a record with Bach and Mozart into space?

His yearning to understand the cosmos wasn't limited to the expansive blackness beyond Earth's atmosphere. He believed everyone should share in the wonders of science and the universe -- a legacy that lives on through colleagues, fans and family to this day. Some present-day admirers mix Sagan's musings in music form ("A Glorious Dawn," anyone?). Humbly, Sagan reminded us that we too are made of "star stuff."

Perhaps the phrase "billions upon billions of stars" conjures up breath-taking images from the PBS series "Cosmos." Or you may be familiar with Sagan's skeptical attitude or search for extraterrestrial life. He also left his mark on political and religious discussions, recognizing that science affects many facets of life. Yet one Sagan biographer notes that the greatest dichotomy of Sagan's life was Sagan himself -- he was both prophet and skeptic; someone who teetered between being uplifted by creativity and grounded by the facts [source: Davidson].

Let's get to know the man whose idea of fun entailed characterizing the mysterious surfaces of planets, describing the chemistry required for life and pondering humans' place in the enormous universe. His legacy spans the space program, academia and popular media, and it all began in Brooklyn.