Astro-navigation from Square One to Ocean-master begins at the very beginning of this relatively complex subject and progresses logically through all the required 'astro skills'. Each new concept builds on UNDERSTANDING with no 'learning by rote'. A 130-word glossary, 160 diagrams and 40 worked examples, all using 2011 Sun, Moon, planet and star data, are contained in 308 pages. The parts relevant to the RYA Yachtmaster Ocean syllabus are identified. In nine sections the book begins with the basic concepts of great circles, Greenwich Hour Angle and Declination, describing a heavenly body's position on the celestial sphere which, with the observer's zenith, a body's geographical position and a measured altitude of that body, produces a unique position circle. Greenwich Mean Time and its link to longitude and then latitude estimation from the Sun's meridian passage are explored. Section 2 details the correction to achieve an observed altitude and the need for a calculated from a chosen position, permitting an intercept to be found on the azimuth of the observed body, using the mathematical solution to the PZX triangle. Section 3 explores the design, use and error-correction of the sextant and Section 4, the myriad of navigation tables including Rapid (Air) and Marine Sight Reduction Tables. Section 5 details the Sun, time, GMT and the equation of time. Sections 6,7,8 and 9 each detail the particularities of using the Sun, Moon, planets and stars, using specific examples including Sun-run-Sun, Rapid Sight Reduction Tables for seven chosen stars and Polaris for latitude estimation. The Appendix explores the mathematics of the cosine navigation formula, its conversion for calculator and plotting sheets for ocean position-plotting.