# NavList:

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

**Re: 'The Complete On-Board Celestial Navigator' book**

**From:**Peter Fogg

**Date:**2003 Mar 30, 06:56 +1000

('The dog ate my homework' - the electronic gremlins have consigned my original message to some black hole, its a great mystery, so this is another attempt ..) Gerard Mittelstaedt wrote: > Hi, > I ... found > The Complete On-Board Celestial Navigator > by George G Bennett isbn = 0-07-139657-8 > listed on Amazon.com > > The book is organized in 11 chapters, that can > be logically organized into sections on > - How to > - Almanac data, including > Stars & Aries, Sun & planets, Moon > - "planning observations" > - sextant corrections > - the Marcq St.Hilaire Method - > and various tables and forms. Apart from what you have mentioned, it also has: * 'Prediction and Identification' tables for stars and also Sun, Moon and planets, * Graphs for finding the Local Apparent Time of sunrise and sunset, * The same thing for LAT of morning and evening Civil Twilight, * 3 methods for calculating Azimuth, * Star charts for the southern and northern sky * An explanation of using Amplitude for checking a compass * Latitude using Polaris * Latitude using noon Sun (called 'Meridian Observations') * A page titled 'Calculator Interpolation' * 'Change of Altitude in 5 Minutes of Time' * 'Sextant Altitude Observations' these last two are the method and blank form for plotting a series of observations against the body's apparent rise or fall over 5 minutes. A wonderful method to plot a series of sights graphically, can indicate better data than any of the individual sights. As always, there is an explanation and a worked out example to follow. > > The Almanac section of "The Complete..." seems > to be abbreviated, and probably needs a lot of > interpolation for use. In the almanac section, first comes the: 'GHA for Aries' for each day, incl. time of day correction. Opposite each page is an 'Index of Bright Stars' with SHA and Dec, the Dip correction and the altitude corr., everything you need here is on the two facing pages. 'Sun and Planets' section is similar, GHA and Dec listed for each day, the 'v' and 'd' corrections and interpolations are found at the end of these pages. The Moon has the GHA and Dec listed for each 6 hours of GMT, again the interpolation pages for 'v' and 'd' and altitude. corr. HP etc are at the end of this section. You can either look up the corrections and interpolations or use a calculator to work them out more accurately, its all there. As for abbreviated, the data in the almanac and also the sight reduction method is presented to the nearest minute of arc. This enables it all to fit into such a compact format and does simplify things greatly. Recently on this list there was a discussion of how accurate CN could be. For a surveyor using a theodolite on a tripod that can be very accurate indeed, but for a navigator on a small boat the greatest impediment to accuracy is likely to be the boat's movement. Being able to work out an intercept to the nearest nautical mile, using just the one book (and its photocopied forms) fairly simply and quickly, needing only simple addition, seems to be the book's aim. The sight reduction method uses a DR, a position in degrees and minutes of arc. Compared to a method that uses an assumed position to the nearest whole degrees the intercepts tend to be shorter and thus indicate more accurately the position. With this method, should the DR turn out to be a long way from the fix, the sight reduction process can be repeated using the fix as an improved DR and the new intercepts should be much shorter and thus more accurate. Only simple addition is needed to process the data through the sight reduction method, and the form is provided. It starts with the local day and date and finishes with the intercept and azimuth. Along the way it has handy reminders where they are helpful (+Slow, -Fast and +West, -East for example) and as well the book comes with a page of step by step instructions that walk you through the process of sight reduction, and a suggestion that you photocopy this page, put the page of time/degree conversions on the other side, and cover them with plastic. This sheet then becomes a handy bookmark and is often referred to. I am not aware of any other book that compares with this one, that wraps up everything the navigator could need for practical CN (except the sextant!) in the one compact package. It can even be used as a textbook, as in 6 short chapters it goes through the theory and method using worked out examples at each stage. It does assume a basic understanding of latitude and longitude and plotting; let's say the skills of coastal navigation as a starting point. It lies open flat, much appreciated on-board (I once was silly enough to buy a paperback Nautical Almanac, it drove me mad trying to extract data from it - I never had enough hands!) a small point but typical, I think, of how well this book has been planned for practical use. > > The price was modest (just under $20.00 US), > and I bought it. Half your luck (says me sourly) books are much more expensive here. Just as well I think its worth every penny. Good luck with it, Gerard and everyone else who has it, let us know how you find it with a little more familiarity and practice. Glossary CN Celestial Navigation GHA Greenwich Hour angle LAT Local Apparent Time SHA Sidereal Hour Angle Dec Declination DR Deduced Reckoning; a calculated position advanced from a previous fix. fix Postion established by CN or some other method