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Published Date

January 2004

Celestial Navigation (ASNAV)

(Excludes any applicable taxes)

This program calculates your position by means of observations of stars or planets (a nautical almanac is not required). The user enters only his estimated position and the sextant altitudes of stars, planets, sun or moon. The program computes and plots the most probable position and an ellipse of probability around it, together with the lines of position (LOPs). Also includes applications for: star fix wizard, azimuth, rhumb line, great circle and ETA.

Compatible with Windows 10.



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Celestial Navigation is a unique package for the computation of sights and sight reduction by conducting the following statistical analysis:

  • each observation can include some minor errors, perhaps due to a poor horizon, clouds or the ship rolling while taking your observations. It is difficult to estimate for yourself the quality of a given observation due to the fact that these small errors generally counterbalance each other. For this reason the ASNAv program gives a certain weight to each observation according to its reliability  in the normal law model.

  • very often an observer will repeat the same constant error for each observation (uncorrected sextant index error and personal error etc). This systematic error of the observer can be computed and eliminated

  • the program can also correct the assumed course and speed if sufficient observations are provided (this is done in exactly the same manner that the GPS gives a course and speed of the vessel if sufficient satellites are visible).

Additional Features:

     - Star fix wizard to help prepare for star observations
     - Compass errors - Azimuth calculations
     - Single rhumb line, great circle and composite great circle calculations on ellipsoid (e.g. WGS-84) and not only on a sphere
     - Comprehensive manual (help file) with an introduction to celestial navigation

See this website for more information on the celestial navigation.

Celestial Navigation (ASNAv) is an astronomic navigation program written by Johan Machtelinckx while serving as Merchant Navy officer in the Belgian fleet.

The user enters only his estimated position and sextant altitudes of heavenly bodies (stars, planets, sun, moon). The program computes and plots (see example) the most probable position and an ellipse of probability around it, together with the lines of position (LOPs).

A nautical almanac is not required.
ASNAv is something new in the world of celestial navigation programs - it is designed by a seaman for seamen.

The program aims to be a practical option as backup of the today omnipresent GPS. This means that ASNAv aims to reduce additional workload to a minimum. There is little time required outswith the time necessary to take the observations themselves.

ASNAv also has the following characteristics:

  • It includes an accurate nautical almanac without limit of time.

  • It computes rhumb lines on an ellipsoid (e.g. WGS-84) and not only on a sphere.

  • Great circles are also calculated on an ellipsoid (including composite sailing).

  • It is able to find the compass error by means of an azimuth observation

  • A star fix wizard helps to prepare the stars observations

  • It computes ETA (Estimated Time of Arrival) in local time.

Title: Celestial Navigation (ASNAV)
Product Code: 4035
Published Date: January 2004
Weight: 0.20 kg

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A network version is available, contact us for details.

Corrections and improvements since release 0.9

List of bugs corrected on the ASNAv 1.0 version:

the Star Fix Wizard didn't take into account the user's selection of stars and was sometimes crashing the program ("Subscript Out of Range" error) when going back from Step 4 to Step 3. This is fixed.

the Star Fix Wizard didn't take into account the height of observer eye. The stars altitudes displayed were calculated altitudes. Now, these are sextant altitudes, which means that the necessary corrections are applied (in a reverse way that usual) to obtain sextant altitudes from the calculated altitudes assumed to be the true altitudes.

it was sometimes no more possible to close the Star Fix Wizard. This is fixed.

if the program used a truncated routine due to an insufficient time spread, then the maximum time between the observations was sometimes not displayed. This is fixed.

if a wrong time of observation was entered in the grid (typing error like 22 Nov 1999 220012), the program crashed. This is fixed.

if the user tried to erase an observation by just deleting the content of the 4 cells (not by deleting the entire line) and after that he asked to compute the results, then the results were computed only with the observations above the deleted line. In addition, after this computation, the grid data's became invalid. This is fixed.

in the observations grid, the tooltip "Enter time in GMT" was displayed for the entire grid; now, it is displayed for the first column only.

if "Options - Preferences - Intercepts - Compute all the intercepts with the given estimated position" was checked, the estimated position given by the user was always used, even if the time of the given estimated position was different than the time of the true position to compute. This is fixed. If this option is checked, the given estimated position is now translated at the time of the true position before calculation of all the intercepts with this estimated position (if the option is not checked, the intercepts are calculated with an estimated position translated for each observation at the time of the observation).
Another small fix : if the same option is checked, the distance to transfer each LOP is now displayed.

the azimuth calculation sheet was erased if the focus was temporary given to another program. This is fixed.

the system time was sometimes wrongly displayed in the Options - Preferences - Time tab. This is fixed.
Note that if you want to set your computer clock in GMT time, you need to select "(GMT) Monrovia, Casablanca" which is not a Daylight Saving Time (DST) zone. If you select "(GMT) Greenwich Mean Time ; Dublin, Edinburg, London, Lisbon", the internal GMT time will be one hour earlier than your computer clock time when DST is active.

the four pictures at the bottom of the screen (used to select one of the functions of ASNAv) were still active in various wrong situations (e.g. under the result screens or with the azimuth form displayed). This is fixed.

the middle latitude chart used to display the MPP and the LOPs had a correct scale on the screen but an incorrect scale on some printers. This is fixed.

List of improvements made to ASNAv 1.0:

the files with the observations data's are now compatible whatever computer used to create them (US system or local system like French).

the azimuth calculation sheet used symbols peculiar to Belgian ship (like /v or Cv). This is changed to more understandable terms (like true bearing, true course, ...).

the Star Fix Wizard identifies the [F5] key, reduces itself and gives way to the "Store current time" dialog box.

the splash screen can now be escaped by pressing any key.

Corrections made to ASNAv 1.01:

one of the last bug corrections made to ASNAv 1.0 caused a side-effect which provoked a crash when opening Utilities - ETA Calculation and which prevented from changing the system time in Options - Preferences - Time. This is corrected (24 May 2000).

to ease the installation process, the self-extractible zipped file asnazip.exe was replaced on 28 May 2000 by asna_ins.exe, a zipped file able to install the program automatically.

Corrections made to ASNAv 1.02:

there was a wrong graphic display in the South hemisphere. This is fixed.

on a NT system, the program was not releasing resources when closed with the upper right close box [X]. This is fixed. 

it was possible to enter only a time of observation, without any date (e.g. 08:03:12). Due to the internal format for storing dates, the program used in this case the 30 Dec 1899 (in our example, 30 Dec 1899 08:03:12), which gave a very, very long sailing time (!) and a rhumb line calculation error (all the rhumb lines are finally crossing the Pole).  This is fixed.


the numeric display of the results used symbols peculiar to Belgian ship (like Hi for Hs or Hv for Ho). The terms of the Nautical Almanac are now in force.


Corrections & improvements made to ASNAv 1.1:

the moon is now supported.

the accuracy of the internal Nautical Almanac for Saturn is increased to the level of the other planets.

the azimuth calculation sheet is able to list all the visible stars at the user position (with sorting facilities).

a new date / time input system is implemented.

sometimes the great circle routine caused errors. This is fixed.

the observations data's entry form now allows to choose directly between round of sight or running fix for comparison with manual calculations. This is avoiding the use of the Options - Preferences... menu.

wrong altitudes (e.g. 40°69'.2) or instrumental errors entered in the observations grid could crash the program. This is fixed.

after accessing an observations file in a sub-directory, the help file could not be found anymore if called by the menu. This is fixed.

various "cosmetic" changes.


Corrections made to ASNAv 1.18:

when the user rejected manually the option "Correct the course and speed if enough observations", the program still tried to correct them if possible. This is fixed.

escaping the correction of sextant altitude or instrumental error in the grid with <Esc> gave a false indication of missing data. This is corrected.

entering a longitude interval of 00°00' for great circle calculation caused an error. This is fixed.

the visible stars at the user position were not displayed from the azimuth calculation sheet when the user was leaving the Star Fix Wizard by <Cancel> before. This is corrected.

the azimuth calculation sheet listed the altitude of the center of the moon for MOONUPP (upper limb of the moon) and MOONLOW (lower limb of the moon). The same for the Sun. The correct altitudes are now displayed in both cases.

the menu 'Astro Position' - 'Erase datas' can be used to go back to the main page.

new help file in html format with celestial navigation manual.

Corrections & improvements made to ASNAv 1.19:

enhanced html help file.

the program could crash when displaying the numeric results if no default printer driver was installed on the user machine. This is fixed.

the splash screen is replaced by a text box on computers still using Windows 95 to avoid any display problem.

it isn't possible anymore to enter the same departure and arrival positions for great circle calculations (1.191).

the ETA calculation sheet minimum speed, maximum speed and interval are limited to values which cannot generate errors (1.191).

small corrections of editing behaviour in great circle and ETA calculation sheets (1.192).

rhumb line calculations could fail if the arrival and departure latitudes were very close but not exactly equal (special case already taken into account). This happened sometimes during the calculations of intermediate rhumb lines connecting the points of a great circle. This is fixed (1.192).

the default time used in the observations grid is:  when the user press [Space] or double click the cell:  the computer system time saved by the stopwatch icon or [F5]
 if not valid, the previous time in the cell
 if not valid, the time of the same cell in the previous row
 if not valid, the time of the estimated position
 if not valid, the current computer date

 when the user press another key:  the last edited value
 if not valid, the current computer date (but in both cases the first digit is replaced by the pressed key if possible) (1.192).


the numeric results sheet is now displaying the original course and speed (before possible corrections by ASNAv algorithm). These original course and speed are also saved in the observations file (*.OBS) instead of the corrected course and speed (1.192).

the fields accessible by [TAB] in the observations input form (tab 1) are changed (1.193).

the Vertex position calculation with full accuracy could fail if very close to the departure or arrival position. This is fixed (1.194).

the rhumb line calculation with full accuracy could fail if the departure and arrival position were nearly equal. This is corrected (1.194).

help file amended (1.194).

Corrections & improvements made to ASNAv 1.2:

various compatibility problems in very specific cases solved (problems involving the splash screen video, the formatting of the numeric results, the communication with printers, some international settings)

help file amended.