The free math library Mathlib, written by Rick Huebner, is required; a copy is included for your convenience.
For a complete celestial navigation package, including perpetual nautical almanac, try CelestNav from Mobile Geographics. Download the free demo at http://www.mobilegeographics.com/celestnav/.
Buy your celestial navigation books and tables here.
MG229 is a free program, released to introduce you to our products. Current version is 1.1, released July 20, 2000.
Enter celestial body's GHA (Greenwich Hour Angle) and declination (you must obtain these values from the Nautical Almanac).
If "Round AP" is checked, AP (assumed position) is rounded to nearest whole degree of latitude, and to a longitude chosen to give a whole degree LHA. Otherwise AP is simply DR.
Body's LHA (local hour angle) is computed automatically from GHA and DR longitude if "Calc from GHA" is checked.
To match the tabulated entries in HO 229, check "Round AP", uncheck "Calc from GHA", and enter LHA manually instead of GHA.
Hc and Ho are the predicted (Hc) and observed (Ho) altitudes of the celestial body.
"Contrary" means that Declination and Latitude are in opposite hemispheres; "Same" means they are in the same hemisphere.
To plot the LOP, begin at the AP. LOP is perpendicular to the Azim value, at the given distance from the AP.
The "DDD", "DMM", and "DMS" pushbuttons select among decimal degrees, degrees and decimal minutes, or degrees/minutes/decimal seconds.
The "° ' ''" button cycles through the degrees, minutes, and seconds fields. You can also tap on a field to select it.
The "000" button truncates the current field to an integer, and zero-fills the fields to the right of the current field.
Use the S/N, E/W, or +/- pushbuttons to change the sign of your angle.
You observe in your sextant the star Antares. After correcting for index error, dip, and atmospheric conditions, you calculate a height Ho of 20° 19.4'. Enter that value for Ho.
Check the "Calc from GHA?" box to enter your GHA and have MG229 compute your LHA. The Nautical Almanac tells you that Antares's GHA is 334° 26.1', and declination S 26° 25.9'. Enter those values for GHA and Decl. Since your DR latitude is north and the star's declination is south, MG229 displays "contrary". Your LHA, as computed by MG229, is 319° 00.0'.
Check the "Round AP" box This will display an AP (assumed position) of W 15° 26.1', N 32° 00.0'
MG229 displays a value of 19° 42.5' for Hc, and azimuth of 141°, with an intercept of 36.9 nautical miles "toward".
To plot this LOP on your paper chart, begin from the displayed AP position. Draw a line from your AP on bearing 141. At a point on that line 36.9 nm from the AP, place a dot, the intercept point. Draw a perpendicular to your first line (the azimuth line), through the intercept point. Your position was somewhere along that line.
Now turn to volume 3 of HO 229, page 85 (the page that lists LHA of 319, contrary latitude/declination names). Look under the column for latitude 32°. Interpolation between the values for declination 26 and 27 gives an Hc of 19° 42.1', and both Z and azimuth of 141.4°.
Your screen should look like the one at the top of the page.
Last modified: Sun Apr 20 11:32:49 PDT 2003