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The section on Celestial Navigation originally was the main page on this web site. As a consequence, this part of my web pages has some older parts, which are not yet completely 'integrated' in the rest of the documents. Since my interest is primary on the practical side of Celestial Navigation, the more theoretical issues are not at all or only basically covered. Some of this basic material is quoted from other web sites. When using quoted material this is explicitly mentioned including the web links I used to obtain that information. However, since most of this material is already more than ten years old - which is a rather long time in the Web - some of these links may be outdated!

The following is a short overview of how this project evolved and additionally some important notes on how the information of these web pages may be used.

Project Development

Nautical Almanac

The first part of the project was the Nautical Almanac, which is based on the ephemeris data available from the Jet Propulsion Laboratory at the NASA. The driving idea to make a Nautical Almanac available from an internet server, was that many hobby sailors like myself, are practising Celestial Navigation for only a couple of days or weeks a year.
So, if only a couple of pages from the commercially available Nautical Publications are needed, why not try to generate these pages in a simple way and make them available to the interested (internet) community.

From this site the Nautical Almanac is available in two forms:

  • an interactive form supplying the Almanac Data of one (selectable) celestial body for 6 successive days in HTML format
  • a compiled form of the Nautical Almanac for a complete year as PDF file (ca. 1.5 Mbyte). This Nautical Almanac can now be downloaded in 5 separate parts to reduce web traffic and save transfer costs. See the "Download Section" for more information.

Interpolation Tables

The Interpolation Tables available here are designed to be used for both interpolation of the Nautical Almanac data (GHA and Declination) as well as for the interpolation of the data from the Sight Reduction Tables (Altitude). In order to obtain the highest possible accuracy, I decided to use a logarithmic numeric method for interpolation.

These Tables are also available as PDF file from the "Download Section".

Correction Tables for Sextant Altitudes

The next step was to find the formulas and mathematical models for the corrections, which have to be made on the measured altitudes in order to align these measurements taken from the real world with the calculated data obtained from an idealized mathematical model of the universe used for the Nautical Almanac.
These corrections are available from the "Correction Tables for Sextant Altitudes" or also as PDF document from the "Download Section".

Sight Reduction Tables

Finally, I included the "Sight Reduction Tables" to determine calculated altitudes without having to use an electronic calculator.

These tables are similar to the tables published by the (former) "Defence Mapping Agency of the Hydrographic/Topographic Center" as "H.O.229".

Since the Nautical Almanac available from this site only contains information on the Sun, Moon, Venus, Mars, Jupiter and Saturn, the range of the Declination in the Sight Reduction Tables available here is consistently limited to 0°-29°, reducing the volume to 1/3rd of the full-range volume.

The Sight Reduction Tables covering Latitudes from 0° to 69° are available as interactive Tables or as 14-volume PDF document from the "Download Section".

Source codes

The codes of the programs used for generating the Ephemerides of the Nautical Almanac as well as the program used for generating the Sight Reduction Tables can be downloaded for personal use.
This software package does not include the JPL Ephemerides but consists of:

  • the NOVAS subroutines
  • the program codes of David Hoffman for generating and manipulating the binary ephemeris file(s)
  • my own source codes for Nautical Almanac, Sight Reduction Tables, Sextant Correction Tables and Interpolation Tables.

The package is called CN_code.tgz and comes as a "gzipped-tar-archive" (850 Kbyte). More information on how to extract this archive and on compilation of the C-code is available from the "Notes on the C programs used to calculate the Ephemerides".

Terms of Usage

These Web Pages do not pretend to be a complete guide to Celestial Navigation. The principal purpose of these Web Pages is to serve as my personal source of information for practising Celestial Navigation. I would of course enjoy it very much if other people interested Celestial Navigation may find some useful information here.

Notice however that there is no guarantee that the information available from this site is correct. Especially many of the tabulated information is generated with computer programs, which may still contain some uncovered bugs. All the data in the Tables and Almanacs is believed to be accurate but absolutely no warranty is given for it's correctness.

Use the navigation related data and tables available from this web site only for training and exercising! If some data from this site is used for true navigation, please ALWAYS verify the obtained position with another - more reliable - method of navigation.

Cover  <<  Sail Away  <<  Celestial Navigation  << . .  >>  Celestial Navigation and GPS last updated: 03-Feb-2004