## Celestial Navigation in the GPS AgeMany books on celestial navigation take shortcuts in explaining concepts; incorrect diagrams and discussion are often used for the sake of moving the student along quickly. This book tells the true story-and the whole story. It conveys celestial navigation concepts clearly and in the shortest possible time.It's tailored for navigation in the GPS age-a time of computers, calculators, and web resources. Although it covers all of the traditional methods of 'working a sight, ' the primary thrust is using the (under $10) scientific calculator. By using equations that you key into your calculator, this book guides you toward a better understanding of the concepts of celestial navigation.You will learn novel ways to plot lines of position, ways to check your sextant accurately by star sights, and how to tell what time it is from a moon sight. The many appendices are a treasure of references and explanations of abstract ideas. Celestial Navigation is a crucial skill for the offshore navigator to know, this book provides the shortest path to that knowledge. |

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### Contents

Other Lunars | 97 |

THE ALTITUDE OBSERVATIONS | 99 |

The Sextant | 100 |

The Telescope | 102 |

Telescopes with Traditional Horizon Mirrors | 105 |

Sextant Checks and Adjustments | 109 |

The Index Mirror | 110 |

The Horizon Mirror | 112 |

13 | |

14 | |

The Navigation Triangle | 16 |

The Local Hour Angle | 18 |

Azimuth Angle and Azimuth | 19 |

Three Plotting Methods | 20 |

THE ST HILAIRE METHOD | 25 |

The Straight Line Approximation | 27 |

The Error | 28 |

Why St Hilaire? | 30 |

THE NAUTICAL ALMANACAN OVERVIEW | 31 |

The Altitude Corrections | 32 |

SUN SIGHT REDUCTIONS | 35 |

Using Direct Computation | 37 |

Altitude Corrections | 39 |

The GHA and Declination Increments | 40 |

The LHA | 41 |

The Triangle Solution | 42 |

Using Tables | 44 |

The Solution Using HO249 | 45 |

The Solution Using HO229 | 48 |

Four Examples of Sun Sights | 49 |

SIGHTS OF OTHER CELESTIAL BODIES | 55 |

The Planets | 57 |

The Stars | 59 |

Star Sights by Direct Calculation | 60 |

Star Sights by HO249 | 62 |

The Moon | 63 |

SPECIAL SIGHTS | 67 |

Meridian Sights | 69 |

Latitude without Meridian Shots or UT | 70 |

Latitude and Longitude from Meridian Sights | 71 |

Longitude from Altitude and Latitude | 73 |

Position without St Hilaire | 77 |

LUNAR DISTANCE SIGHTS | 81 |

Taking the Lunar Sight | 83 |

The Distance Clearing Concept | 85 |

Clearing the Lunar Distance | 88 |

The Sight Reduction | 90 |

A Lunar Example | 94 |

Accuracy | 95 |

So Why Lunars Today? | 96 |

Index Error | 113 |

Backlash | 114 |

Sextant Arc Error | 115 |

Taking a Sight | 117 |

Averaging Sights | 121 |

Altitude Corrections | 124 |

Refraction | 125 |

Parallax | 126 |

OPERATIONS AT SEA | 129 |

Celestial with GPS | 130 |

Those Special Sights | 133 |

Plotting | 134 |

Estimated Positions and Running Fixes | 135 |

Special LOP Orientations | 138 |

Great Circle Sailings | 141 |

Time | 143 |

Accuracy | 144 |

TABLES CALCULATORS AND COMPUTERS THE DEBATE | 147 |

Calculators and Computers | 151 |

INSIGHTS FROM THE NAVIGATION TRIANGLE | 155 |

The Azimuth Rules | 158 |

Special Cases of the Azimuth Equation | 160 |

EXERCISES FOR UNDERSTANDING AND CONFIDENCE | 163 |

Sight Reduction and the Navigation Triangle | 165 |

Navigational Astronomy | 175 |

Courses Distances and Charts | 181 |

Lunar Distances | 185 |

Computer Programming | 189 |

APPENDICES | 195 |

APPENDIX A NAVIGATION TRIANGLE FORMULAE | 196 |

APPENDIX B CALCULATOR KEYSTROKES | 200 |

APPENDIX C EXCERPTS FROM THE NAUTICAL ALMANAC | 207 |

EXCERPTS FROM HO229 | 216 |

SIGHT REDUCTION WORKSHEETS | 230 |

APPENDIX F CONCEPTS IN PLANE GEOMETRY | 237 |

APPENDIX G SEXTANT ARC ERROR TABLES | 239 |

APPENDIX H DIP SHORT OF HORIZON | 253 |

APPENDIX I A BRIEF HISTORY OF NAVIGATION | 254 |

APPENDIX J ANNOTATED BIBLIOGRAPHY | 260 |

ABBREVIATIONS USED IN THE TEXT | 265 |

267 | |

### Common terms and phrases

accuracy adjustment altitude and azimuth Appendix Aries azimuth angle azimuth equation azimuth rules Celestaire celestial bodies celestial navigation chart CM CM CM CM CN CM SO CM CN CM CN CN CN CO CO CO co-altitude Corr cosine daily pages declination direct calculation discussed DR position equal-altitude g co g great-circle distance Hilaire method horizon mirror hour angle index mirror interpolation keystrokes latitude latitude and longitude LDSD limb lunar distance minutes of arc moon moon's Nautical Almanac navigation triangle o-o o-o o-o observed altitude observer's parallax planets plotting Polaris refraction rH CM rH CO rH rH rH rH running fixes semidiameter sextant ship's shown in Figure Sight Reduction Tables sp so sp sp sp star fix sun sight sun's GP tabulated telescope tx CO tx tx tx tx worksheet