Useful tools

A number of sight reduction software programs are available for free on the Internet. See and A Google search for “navigation calculators” will bring up many more.

OpenCPN, a popular chartplotter software for Linux, Mac OS X and Windows, offers a celestial navigation plug-in that features ephemeris calculation, sight reduction and automatic LOP plots You can find it at

CelNav, a free software application developed by the author, was designed to specifically support the method described in this article. In addition to automating sight reduction, it includes an electronic almanac and the ability to log sight data in a spreadsheet format for later analysis. CelNav is available stand-alone at or as part of Navigatrix, a complete operating system and software tool set for use on a boat (see

An invaluable tool for anyone involved in celestial navigation is Stellarium, an electronic planetarium that makes it very easy to identify suitable stars and planets for a fix. Stellarium is available at

For those who want to learn more about celestial navigation, there are numerous tutorials available on the Internet — for example, If you are not afraid of a bit of math, Henning Umland’s A Short Guide to Celestial Navigation is an excellent source (available at and well suited to complement some of the more “how-to”-oriented guides. 

An excellent book that effortlessly introduces the theory without falling short on the practical application is John Karl’s Celestial Navigation in the GPS Age, Paradise Cay Publications 2011.

By Ocean Navigator