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.

About the Excel file

The Excel file containing the Astronav software is a Microsoft Office 2007 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.

When you click on the Excel version “for Excel 97-2003”, "Google Documents" displays its own distorted version of the Excel file (.xls). To get the original file, click on the “file” tab and download it.

Fair winds and navigation!

Paul Chevrette

P.S.: You may contact me via 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.


Sunday, March 2, 2014

New version 11.0.8

I found out that on my new computer with Windows 8.1 and Office 2013, some of the macros in AstronavXls were not working properly, if at all. I had to do some corrections in the Excel VBA software to fix the problems. Now, everything seems OK, at least on my computer... Please, let me know via the "comments" indicator if you find anything wrong.


Monday, November 11, 2013

Version 11.0.7

I found there was a bug with the RESET button in the previous version. It did reset the wrong cells and in the process erased some important formulas. If you did not use the reset button but changed the input cells directly from the previous entries, there was no problem. This version corrects the bug.

Just as a reminder, it is possible to use the software to process midday or meridian transit sights. Once you have filled the «Time of observation» and «Observed celestial body» boxes, convert the calculated «GHA corrected» to equivalent East or West longitude and enter it in place of your «Assumed Position». Then, you can read your actual position at the bottom of the «LOP plot» sheet, as the «LatLP1» and LonLP1» coordinates (or whichever sight number you used).

I am working on a way to make this more «user friendly».


Wednesday, March 6, 2013

Version 11.0.6

An additional parameter, the Local Hour Angle of Aries (LHAy), appears in the Observed Celestial Body block. This parameter can also be seen as the Right Ascension of the observer's meridian with respect to the first point of Aries, a parameter required for the proper setting of a star finder. Combined with the sextant measured altitude and the azimuth of the observed celestial body, the latest can be identified on a star finder.

Thursday, November 29, 2012

Version 11.0.5

The graph showing the azimuth lines and the circles of position was modified to add a star (asterisk) on the azimuth lines, on the edge of the graph, to indicate the direction of the observed celestial body. The star appears, whatever the scale factor, which was not the case in previous versions. Also, the linewidth of the azimuth lines was thinned in order to reduce the cluttering of the graph.

Saturday, November 24, 2012

Version 11.0.4

This version 11.0.4 introduces minor additions to the legends of the various graphes in order to improve their compréhension. Also, some modifications to the GHA interpolator for a reading in degrees-minutes, as well as in decimals.
It will always be a pleasure for me to answer your questions, or take your suggestions.

Wednesday, March 28, 2012

Version 11.0.3

A checkbox has been added in the "LOP plot" worksheet to give the choice to the user of displaying or not the linear approximations to the "circles of position", used to find their intersections and the observer's position. That helps clarifying the graph.
Other improvements were made to remove a first erratic step after changing the scale of the chart, when using the chart-centering spin-buttons.
Finally, the "User manual" was completely reviewed.

Version 11.0

Significant changes have been made in this version to improve the efficiency but the major change concerns the elimination of the 3rd-order polynomial approximations to the circles of position, to come back to a linear approximation, in order to find the intersection points.
The solution of two 3rd-order polynomials is very complex, and I can't guarantee that it will work in all cases. In fact, I found cases where it didn't. So, I am back to linear interpolation, enhanced by an automatic iterative process to make sure the linear approximations converge to a solution tangential to the curves in the vicinity of their intersection point. Hence, the intersection points are found with as much, if not more accuracy than with the polynomials, and it works in all cases (I hope...!!!). If you find any case where the program fails, please, let me know.