Introduction to this site

This celestial navigation software allows the reduction of sextant sights. The software is based on macro-enabled Microsoft Excel Worksheets. With primary input data from the Nautical Almanac, it gives a graphical representation of the various parameters used in the solution of the spherical navigation triangle, while minimizing the need of correction tables. Up to three sights can be processed and the results are plotted, showing azimuth lines and circles of position. The intersections of the circles of position are computed, as well as the resulting mean position.

One must keep in mind that electronic navigation aids (GPS and others), although indispensable nowadays because of their efficiency and accuracy, will always be subject to technology contingencies, their status of maintenance and, not the least, the variability of the world mutual trust. Celestial navigation remains above all those constraints… And when nothing else works, the good old sextant will always come in handy… as long as one knows how to use it!

I developed this software in an attempt to put together the knowledge acquired from navigation courses from the Canadian Power Squadron, and I offer it for free to all who have an interest in sextant celestial navigation as a challenge, to preserve the knowledge and know-how, or out of sheer curiosity.

Following that line of thought, this software can be considered more as a teaching aid and may contain errors affecting navigation. Hence, there is no warranty pertaining to the accuracy and the results obtained from using the product.

How to download AstronavXls and other documents

- In the “Download Documents” section, to the right, click on the document you want to download (for example, The latest version of AstronavXls);

- A sample of the file will open on the screen, in a “Google Document” format (this is a non-active file);

- To download the original Excel file, click on the “underscored down arrow” icon on top of the screen; a text box, at the bottom of the screen, will appear and offer you a choice to open the file in Excel mode, or save it to your computer.

- The first time you open the downloaded Excel document, it may open in “protected mode”. Click on “Activate modification”, and save the document.

About the Excel file

The Excel file containing the Astronav software is a Microsoft Office 2013 version with a *.xlsm extension. The “m” in the extension indicates that the file includes “macro functions”. Therefore, the “macro-enable” option must be activated in your Excel setup. The procedure to do so is as follows, once the file is opened:

- Click on the File tab (upper left corner), then «Excel Options/Trust Center/Trust Center Settings/Macro Settings/Enable all macros».

- The procedure may be slightly different in earlier versions of Microsoft Excel.

The file that you are downloading contains, by default and as an example, old sight data taken many years ago, as I was taking the CPS courses. The worksheets may be re-initialized to 0 by clicking on the button «Reset all input data to 0». Nautical Almanac data can be obtained from the following site:
All you have to do is to enter a date and the data for 3 consecutive days will be displayed.

The advantage of the Excel file is that it may be renamed and saved with all your sight data sets, in as many copies as you want. Hence it is good practice to keep a copy as a clean template.

Fair winds and navigation!

Paul Chevrette

Sunday, 6 May 2018

New AstronavXls, version 13.0

In this new version, all three Sight data worksheets have been provided with a check box for meridian passage (midday) sights. Checking the midday sight checkbox on the Sight sheet transfers the corrected GHA value of the celestial body as the Assumed Position (DR) Longitude entry, after conversion to equivalent East or West longitude. The effect is to align the azimuth line of the celestial body to the observer’s meridian at the time of transit. The latitude is found at the intersection of the circle of position with the azimuth line. The observer’s coordinates at transit time are displayed in the Meridian Passage section on the LOP plot worksheet.

Prior to the advent of the GPS, surveyors determined benchmarks coordinates with great accuracy by averaging the meridian transit of several stars, using a theodolite. The new version of AstronavXls allows to test that technique with up to three meridian passage sights, by averaging the obtained coordinates, upon the click of a check box. The technique is not very useful on a moving boat, when one is limited by the time constraint of twilight and a real horizon. However it can very well be applied with an artificial horizon, at a fixed position, where time and available stars are no limits, for the sake of comparison with the more standard method of obtaining a fix. Personally, I made my own artificial horizon with an old 6-inches bathroom mirror, properly leveled using a precision surveyor level, accurate to 2 seconds of arc.

Sunday, 11 March 2018

AstronavXls, version 12.8

Correction of a bug associated with the click box for meridian passage sights.
Two new converter tools were added in the Sight data sheets: a converter from the longitude difference between two meridians to the equivalent time difference in the sun passage, and the reciprocal, a converter from the difference in the sun time passage between two meridians to the equivalent difference in longitude.

Tuesday, 24 October 2017

AstronavXls, version 12.7

Fix of a minor problem occuring in the display of the GHAy projection label, in the time diagram of each "Sight" sheet (the South pole view), whenever the sight type (star, sun, planet or moon) was changed.

Saturday, 14 October 2017

AstronavXls version 12.6

Since AstronavXls plots true circles of position (COP) rather than lines of position (LOP), all reference to LOPs have been modified to COP, except for the name of the plot sheet "LOP Plot" which has been preserved because its is used as a reference marker in the macro commands. I had kept the LOP identification because people are more familiar with the term, but it creates confusion. The equations used to perform the astronomical calculations or the various corrections have been added on the "Sight" sheets, either in a display box, or as comments attached to the appropriate description cells. Some minor bugs or errors have been corrected.

Monday, 2 January 2017

AstronavXls version 12.5

A new block (blue) entitled "Case of Latitude by Polaris Sight", has been added in the 3 "Sight input data sheets". As indicated by the title, this block is activated and shows the Latitude calculation and the azimuth angle results, whenever the name of the "Observed celestial body" is identified as "Polaris". The equation for the correction caused by the offset of Polaris with respect to the North Pole is indicated in the block. More details are given in the updated "AstronavXls user's manual". New Temperature converter (°F to °C) and Pressure converter (in of Hg to millibars) were added in the "Utilities section".

Monday, 10 October 2016

Update of the Sight Series Plotting Sheet

An update of the "Sextant sight series plotting sheet.xlsm" document  allows the "observed altitude" to be always indicated with one decimal accuracy

Friday, 22 April 2016

AstronavXls version 12.4

This new version 12.4 eliminates a bug which happened when a sight azimuth  was in the neighbourhood of 0° (360°) or 180°. The bug manifested itself whenever the line (circle) of position was checked in the checkbox on page "LOP Plot", in order to calculate its intersection point with the circle of position of another sight. Problem corrected.