# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**CN in the GPS Age**

**From:**John Karl

**Date:**2007 Sep 27, 22:05 -0500

Hi Folks,

Frank ask for a little info on my
book.

It all started from fairly complete
notes that I had made for a couple of short courses on CN. Then I
decided to expand them even more, just in case other short-course
opportunities cropped up. That's when I got curious about how other
authors treated the subject. I was surprised to learn how different our
approaches were. Most all authors had incorrect (or misleading)
explanations of the "assumed position" used in the St. Hilaire method (or they
didn't attempt an explanation at all), naive or incorrect figures, explained
only one or two kinds of sights, skipped lunars, omitted any computer
applications, had no historical perspective, and had no exercises for the
reader's practice and confidence building.

So I decided it might be worth while to
put my notes into book form. I covered all of the
above topics, while making the book topically
graduated, allowing the beginner to do a full sight reduction by page
40. The book is really all about the same level with only one equation
(the cosine law, naturally) used for all nine types of sight reductions.
But the 72 exercises

__are__graduated in difficulty, started with only high school math and ending with asking the reader to show that my exact lunar-distance clearing equation reduces the commonly used 2nd-order power series. So I hope, perhaps naively, that the book has something for everyone.Nonetheless, from what I've seen of the
NavList, most members will know most everything in the book -- and then
some. Which brings me to the one question I asked in the book that I can't
figure out myself: Why are the tables in H.O. 249 and H.O. 229 ordered
differently? I much prefer H.O. 249's order because latitude changes
slowly at sea, while we're always skipping around in LHA.

At the risk of being too wordy on the NavList,
here's the contents of the book:

**Celestial Navigation in the GPS Age**

1. Introduction.

The Fundamental Idea:

The Equal-Altitude Line of Position:

*The Heroic Era, The Story Retold.*The Fundamental Idea:

*An Ancient Observation, the Key concept, The Mariner's Angle*.The Equal-Altitude Line of Position:

*The 3-D Picture, The Limitations of Mechanical Methods, The Only Solution.*2. Plotting the Celestial Navigation
LOP.

Coordinates:

The Navigation Triangle:

Three Plotting Methods:

Coordinates:

*Latitude and Longitude, Greenwich Hour Angle and Declination*.The Navigation Triangle:

*Sun and Earth, The Local Hour Angle, Azimuth Angle and Azimuth*.Three Plotting Methods:

*The Concept, Plotting Variables.*3. The St. Hilaire Method.

*The Captain's Idea, The Straight-line Approximation, The Error, Why St. Hilaire?*4. The Nautical Almanac - an
Overview.

*The Daily Pages, The Altitude Corrections*.5. Sun Sight Reductions.

Using Direct Calculation:

Using Direct Calculation:

*Attitude Corrections, The GHA and Declination, The GHA and Declination Increments, The LHA, The Sketch, The Triangle Solutions.*

Using Tables:*The Solution using H.O. 249, The Solution using H.O. 229.*

Four Examples of Sun Sights.6. Sights of Other Celestial
Bodies:

*Availability, The Planets, The Stars, Star Sights by Direct Calculation, Star Sights by H.O. 249, The Moon.*7. Special Sights.

*Polaris, Meridian Sights, Latitude without Meridian Shots or UT, Latitude and Longitude from Meridian Sights, Longitude from Altitude and Latitude, Time from a Lunar LOP and a Star Fix, Position without St. Hilaire*.8. Lunar Distance Sights.

*The Concept, Taking a Lunar Sight, The Distance Clearing Concept, Clearing the Lunar Distance, The Sight Reduction, A Lunar Example, Accuracy, So Why Lunars Today? Other Lunars.*9. The Altitude Observations.

The Sextant:

Sextant Observations:

Altitude Corrections:

The Sextant:

*The Horizon Mirror, The Telescope, Telescopes with Traditional Horizon Mirrors.*

Sextant Checks and Adjustments:*The Telescope, the Index Mirror, The Horizon Mirror, Index Error, Backlash, Sextant Arc Error*.Sextant Observations:

*Observations at Home, Taking a Sight, Averaging Sights*.Altitude Corrections:

*Dip, Refraction, Upper and Lower Limbs, Parallax.*10. Operations at Sea:

*Celestial before GPS, Celestial with GPS, Those Special Sights, Plotting, Estimated Positions and Running Fixes, Special LOP Orientations, Great-Circle Sailing, Time, Accuracy.*11. Tables, Calculators, and Computers -
the Debate:

*Sight Reduction Tables, Calculators and Computers.*12. Insights from the Navigation
Triangle:

*Equivalent Triangles, The Azimuth Rules, Understanding Inspection Tables, Special Cases of the Azimuth Equation.*13. Exercises for Understanding and
Confidence:

*Sight Reduction and the Navigation Triangle; Navigational Astronomy; Courses, Distances, and Charts; Lunar Distances; Computer Programming.*Appendices:

*A. Navigation Triangle Formulae, B. Calculator Keystrokes, C. The Nautical Almanac, D. Sight Reduction Tables, E. Sight Reduction Worksheets, F. Concepts in Plane Trigonometry, G. Sextant Arc Error Tables, H. Dip Short of Horizon, I. A Brief History of Navigation, J. Annotated Bibliography*..... John Karl

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