^* The index error is regarded as positive when the angle displayed by the instrument is greater than the actual angle.

Description:
This celestial navigation software written in JavaScript performs all calculations necessary to derive a line of position from an observation of the sun. Enter date and time, longitude and latitude of your assumed position, and the altitude displayed by the instrument (sextant or theodolite). It is also possible to enter a zenith distance (measured by some theodolites). Enter the altitude correction parameters, and hit the [Reduce sight] button. The program does the rest. If the dialog boxes for air temperature or atmospheric pressure are left blank, the program calculates with standard values, 10°C (50°F) and 1010 mbar (29.83 in.Hg). Any other blank dialog box is regarded as zero. Use radio buttons and pulldown menus to change program settings. Requires a JavaScript compatible browser like Netscape Navigator 4 or Microsoft Internet Explorer 4 (or later versions).

The internal almanac is based upon formulas given in Astronomical Algorithms by Jean Meeus, and is valid through approx. 2040 (cross-checked with Interactive Computer Ephemeris 0.51 by USNO). The almanac is usually accurate to 0.03'. Beyond 2010, the accuracy will probably slowly decrease but still remain better than 0.1' (comparable to the Nautical Almanac).

The program internally sets dip=0 if any form of an artificial horizon or a zenith distance is chosen. If an external artificial horizon (pan with liquid) is used, the sextant altitude is automatically divided by two after subtracting the index error.

This program is freeware and may be copied and distributed in unmodified form and on a non-profit basis. For your private use, feel free to modifiy the source code according to your requirements. Any commercial distribution requires the author's permission.

Henning Umland

N53-20.1 E9-53.6

e-mail: mail@celnav.de

Check this web site for updated versions: http://www.celnav.de

Warranty disclaimer:

This program is experimental and may still contain bugs and errors, although it has been checked thoroughly. Use at your own risk.