Celestial Navigation   

The GPS was one of the more interesting items that my father bought for his boat (the other was the radar) and learning to use it brought the inevitable comparisons to pre-electronic navigation. As such, I was very excited but not entirely surprised to find a sextant under the Christmas tree the following Christmas. This has been one of my favorite presents and learning to use it has been like walking down a multi-forked path. Many different methods and techniques for celestial navigation have been developed over the years and the sextant has allowed me to explore these many paths all the while learning about the stars, the earth, maps, math, history and above all else - patience.

The link below is a program I wrote (it runs on an HP-28S calculator) to provide quick and accurate ephemeris of the sun without the bulk or cost of the yearly almanac. The program can be used to calculate the declination (Dec) and Greenwhich hour angle (GHA) of the sun for any time between March 1, 1900 and February 28, 2100. If the sun’s observed altitude and your assumed position are also entered the program will also provide the calculated altitude (Hc), azimuth angle (Azn) and intercept (Ic) thus allowing you to plot a line of position.

Please note that the formulas used for this program where sourced from Henning Umland’s excellent website at “home.t-online.de/home/h.umland”. This site is great for people with some mathematics behind them and who want to understand the ‘why’ of celestial navigation (rather than the ‘how’ covered by most books on the subject).

Download HP28S Ephemerides Program (V2).pdf

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