Like many of his scientific colleagues around the nation and around the world, this author was saddened to learn of the death of Carl Sagan on Friday morning, December 20. In his passing the world has lost one of the most energetic and prolific scientists of our era, and one of the strongest voices for science and rationality.

Throughout his more than three decades as a scientist Dr. Sagan attempted to answer the questions which cut to the very core of who and what we are. How did life on the Earth get started? Has life started elsewhere? Are there other solar systems, other worlds, other races somewhere out there in the universe that we may someday get to know? Questions like these have fascinated and piqued the minds of many humans for generations, but thanks in large part to the work of Dr. Sagan, who dedicated his life to pursuing them, today we are beginning to obtain some tentative answers.

Dr. Sagan was instrumental in planning the scientific phases of many of the interplanetary spacecraft that we have launched out to other worlds, beginning with the Mariner series in the 1960s. He was heavily involved in designing the life-search experiments carried by the two Viking spacecraft to Mars in the mid-1970s, and was similarly involved with the two Voyager spacecraft that surveyed the planets in the outer solar system during the 1970s and 1980s. In addition, he devoted much of his research efforts toward understanding the conditions that prevailed on Earth and its vicinity during the early days of the solar system, and how these conditions led to the development of life and Earth and, possibly, elsewhere in the solar system.

Although he made his living as a scientist, Dr. Sagan was also a champion of the triumph of the human spirit, and his writings are full of grand visions of humanity's future which he believed could be fulfilled if humanity would take the initiative to do so. At the same time he grieved over many of the serious issues which humanity must wrestle with today, and was deeply concerned over the possibility that humanity could end its existence through nuclear warfare. During the early 1980s he was a member of a group of scientists who, through the use of computer simulations, discovered the then-unknown devastating effect of nuclear warfare now known under the name of "nuclear winter." While the threat of nuclear warfare has perhaps receded slightly since that time, the concept of "nuclear winter" has taken on a new importance during the past few years, as we have come to realize that some of the same effects could result from the impact of a cometary or asteroidal body upon our Earth.

All of Dr. Sagan's numerous scientific achievements notwithstanding, this author believes that his most important contributions lay in his efforts to bring the wonders of science to the general public. He is perhaps best known for his 1980 PBS television series Cosmos (and the accompanying book of the same title), which sought to introduce the public to the many wonders of the universe around us. Throughout his career he strove to share the many discoveries coming from astronomy with the public, and he always spoke with a strong and passionate voice emphasizing the scientific and rational thought processes involved in interpreting these discoveries. Like many scientists today, this author among them, Dr. Sagan was especially concerned with the prevalence of pseudo-science and anti-science in our society, and he was tireless in always presenting a firm, rationalist viewpoint to counter this.

Dr. Sagan was, undoubtedly, an inspiration to countless individuals, both scientists and lay people alike, and it would be difficult to quantify just how many scientists are active today, striving to answer the same questions that he sought to answer, as a result of his inspiration and efforts. This author, certainly, must be counted among those ranks. At a scientific conference in 1988 this author approached him after he had given a paper to ask him if he could stand to meet one more graduate student "who had always wanted to meet Carl Sagan," and despite the fact that he was enroute to an imminent engagement, he took a few moments of his time to discuss some of the details of his paper. During the years since then this author had additional opportunites to meet and chat with Dr. Sagan at various scientific gatherings, and while the moments were usually fairly brief, they were certainly moments to be treasured.

As we enter the 21st Century facing a host of scientific and technological challenges which we are only now beginning to fathom, it would do us well to pay heed to the voice of rationalism which Dr. Sagan so strongly espoused. In his 1994 book Pale Blue Dot -- the title of which was taken from the Earth's appearance as seen in a photograph taken by the Voyager 1 spacecraft in 1990 from well beyond the orbit of Pluto -- Dr. Sagan challenges us to:

"Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every 'superstar,' every 'supreme leader,' every saint and sinner in the history of our species lived there -- on a mote of dust suspended in a sunbeam."

Carl Sagan, we will miss you.

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