Discovering Pluto is an authoritative account of the exploration of Pluto and its moons, from the first inklings of tentative knowledge through the exciting discoveries made during the flyby of the NASA New Horizons research spacecraft in July 2015. Co-author Dale P. Cruikshank was a co-investigator on the New Horizons mission, while co-author William Sheehan is a noted historian of the Solar System.

Telling the tale of Pluto’s discovery, the authors recount the grand story of our unfolding knowledge of the outer Solar System, from William Herschel’s serendipitous discovery of Uranus in 1781, to the mathematical prediction of Neptune’s existence, to Percival Lowell’s studies of the wayward motions of those giant planets leading to his prediction of another world farther out. Lowell’s efforts led to Clyde Tombaugh’s heroic search and discovery of Pluto—then a mere speck in the telescope—at Lowell Observatory in 1930.

Pluto was finally recognized as the premier body in the Kuiper Belt, the so-called third zone of our Solar System. The first zone contains the terrestrial planets (Mercury through Mars) and the asteroid belt; the second, the gas-giant planets Jupiter through Neptune. The third zone, holding Pluto and the rest of the Kuiper Belt, is the largest and most populous region of the solar system.

Now well beyond Pluto, New Horizons will continue to wend its lonely way through the galaxy, but it is still transmitting data, even today. Its ultimate legacy may be to inspire future generations to uncover more secrets of Pluto, the Solar System, and the Universe.

Twenty years after the Viking missions of the ’70s, we are finally going back to Mars. No fewer than ten missions are planned for the period between 1996 and 2003, and it is likely that human explorers will follow soon after--perhaps by the middle of the twenty-first century. When they do, they will owe much to the Mars of romance, to the early pioneers whose discoveries and disappointments are brought to life in The Planet Mars: A History of Observation and Discovery.

In this timely and vividly written account, William Sheehan traces human fascination with Mars back to the naked-eye observers of the planet. He recalls the early telescopic observers who first made out enigmatic markings and polar caps on its surface. Through lively historical anecdotes, he describes in detail the debate over the so-called canals of Mars, which encouraged speculation that the planet might be inhabited. Finally, Sheehan describes more recent theories about the planet, leading up to the present, when unmanned spacecraft have enabled us to make giant strides in exploration.

Well documented and sparked with human interest, this book will be a useful companion and guide in interpreting the barrage of headlines about Mars that is sure to come over the next few years. Amateurs will appreciate the contributions that have been made to Martian studies by people like themselves, and professionals will find much original material that has never before been published. The American Mars Global Surveyor is scheduled for launch in November 1996, and soon after the American Mars Pathfinder will make its way toward the red planet. A Russian mission consisting of an orbiter and two landers will be launched in October 1997. These space travelers will write a whole new chapter in the dramatic story of Mars, a planet whose exploration has only just begun. Astronomy Book Club main selection and selections of Book-of-the-Month Club and Quality Paperback Book Club.

Astronomy Book of the Year, Mercury Magazine (Astronomical Society of the Pacific)

Do we really know what we see through a telescope? How does the ocular system construct planetary images, and how does the brain interpret them? Drawing on both astronomical and psychological data, William Sheehan offers the first systematic analysis of the perceptual and cognitive factors that go into the initial structuring of a planetary image and its subsequent elaboration. Sheehan details the development of lunar and planetary astronomy, beginning with Galileo’s study of the moon, and focuses particularly on the discover of “canals” on Mars. Through each episode he underscores a perceptual or psychological theme, such as the importance of differences in vision, tachistoscopic perceptual effects, the influence of expectation and suggestion on what one sees, and the social psychology of scientific discovery. Planets and Perception is a provocative book that will intrigue anyone who has ever looked through a telescope. In addition, it offers the psychologically oriented reader a case history in the processes of perception unlike any other in the literature.

Ever since early stargazers discovered that some heavenly bodies wandered among the others, people have been fascinated by the planets. Kepler calculated their orbits from naked-eye observations; Galileo’s telescope made it possible to discern their markings; now observations from spacecraft provide electronically enhanced images that bring these distant worlds even closer.
 
In Worlds in the Sky, William Sheehan gives us a history of this long fascination, weaving together scientific history, anecdotes surrounding planetary discoveries, and the personal reflections of an incurable amateur astronomer. He describes how we arrived at our current understanding of the Moon and the planets and shows how certain individuals in history shaped the world’s knowledge about the Solar System.