The book does an adequate job at teaching the "how to do" celestial navigation, cookbook style. The "theory" section on "how it works" bothers me because it uses a diagram where the earth is shown as flat and the star so close to the earth that it erroneously explains the difference in angle (as you move away from the position directly under the star) by simple trigonometry. In reality, stars are so far away that light rays from them are essentially parallel no matter where you are on earth (the sun and moon are closer and need a parallax correction, but this is a minor adjustment), so the difference in angle is due to the curvature of the earths surface. Understanding that the difference in angle is due to the curvature of the earth is so essential to understanding celestial navigation and why you need spherical trigonometry to solve this, I think the book does a disservice to the student by over simplifying it.