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 Office button (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.

Fair winds and navigation!

Paul Chevrette

P.S.: You may contact me via the "contact form" or the "comments" option below each message. Your comments are not automatically published on the site. I must approve them and their publication is up to my discretion. If you wish to reach me and discuss off-site, please leave your email address within your comment, indicating that you don't want to see it published and I will contact you personnally.


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

New 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

Sunday, 1 February 2015

AstronavXls version 12.3

The Bennet formula, used for the calculation of the refraction correction for sextant altitude observations, was modified for the Smart formula, which gives results closer the the values obtained from the Nautical Almanac.

Thursday, 15 January 2015

Saturday, 10 January 2015

AstronavXls version 12.1

There was an error in sheet "Sight 1". The Horizontal Parallax (HP) correction was not implemented for a moon sight. The problem has been fixed.

Thursday, 14 August 2014

New worksheet for plotting sextant sight series

A new worksheet is available for downloading: "Sextant sight series plotting sheet.xlsm".

This worksheet allows to plot a series of sextant sights on a same celestial body, in order to make a selection of the best sight for a fix, or to find the meridian crossing time in a midday or meridian passage sight.
A polynomial bestfit helps visualizing the trend of the body.
By moving a crosshair with the mouse, one can select the most probable position data for the celestial body, to improve accuracy.


Monday, 4 August 2014

AstronavXls, version 12.0

In this new version 12.0, a green checkbox has been added at the bottom of the input data block, on the first "Sight" sheet. Checking the box indicates that the data entered concern a meridian passage sight, or midday sight. The action taken is to replace the entered "Assumed Longitude" by the "corrected GHA" of the observed celestial body at meridian passage (converted to East/West longitude). This makes the azimuth line of the body directly North/South, in coincidence with the observer's meridian. The corresponding position coordinates of the observer are indicated in a matching green area on the "Plot" sheet.

Since most of the sights taken are midday (meridian passage) sights of the Sun or Moon for a quick one-sight fix, this add-on should be useful. 

The calculated positions from the intersection of multiple LOPs has also been corrected to N/S, E/W coordinates rather than the negative values for South Latitudes and East Longitudes (moreover, there was an error in the conversion, leaving the "minutes" positive).

The version 2.7 of the Great-Circle calculator now presents in dashed lines the part of the curves behind the Earth sphere.