The book presents a comprehensive treatment of celestial navigation based upon the essential foundations of nautical astronomy and spherical trigonometry. Beginning with a discussion of position and time, it proceeds systematically to show how sextant observations coupled with time provide indispensable checks and information on course, distance, and position. Emphasizing computational rather than tabular solutions to sight reduction problems, while basic trigonometric formulae are developed, all computation is done with the most inexpensive hand calculator. The author also stresses the backgrounds of nautical astronomy, beyond the perfunctory routines of sight reduction. The reader, in other words, learns not only what, but why. While the treatment is directed toward the cruising sailor who wishes to plan and undertake oceanic voyages, it is sufficiently comprehensive to fulfill the needs of the professional mariner.