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 now 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.