Artificial horizon for the DIY land navigator

Just in case you break your GPS, here is a suggestion to take sextant sights anywhere, anytime (with a cloudless sky): nothing beats an artificial horizon, made of a solid homemade tripod, an old bathroom mirror with added level adjustment screws, and an equally homemade surveyor's level from a tube obtained through Level Development Ltd, with a precision of 2 arc seconds. Very good reflexion coefficient, but a mirror quality not quite so good. A  first surface mirror would be more adequate to avoid the double reflexion (easily discriminated from brightness difference). Well, another purchase to come...

"Sextant sight series plotting sheet v2"

Modification to the sight series plotting sheet, to allow the removal of data points considered as having an abnormal offset, for an improved bestfit curve. The removal from the curve is obtained by changing to red the Font color for the hour data. The falty point is not erased and can be reestablished by changing the Font color back to black.

AstronavXls, version 13.0

In this new version, all three Sight data worksheets have been provided with a check box for meridian passage (midday) sights. Checking the midday sight checkbox on the Sight sheet transfers the corrected GHA value of the celestial body as the Assumed Position (DR) Longitude entry, after conversion to equivalent East or West longitude. The effect is to align the azimuth line of the celestial body to the observer’s meridian at the time of transit. The latitude is found at the intersection of the circle of position with the azimuth line. The observer’s coordinates at transit time are displayed in the Meridian Passage section on the LOP plot worksheet.

Prior to the advent of the GPS, surveyors determined benchmarks coordinates with great accuracy by averaging the meridian transit of several stars, using a theodolite. The new version of AstronavXls allows to test that technique with up to three meridian passage sights, by averaging the obtained coordinates, upon the click of a check box. The technique is not very useful on a moving boat, when one is limited by the time constraint of twilight and a real horizon. However it can very well be applied with an artificial horizon, at a fixed position, where time and available stars are no limits, for the sake of comparison with the more standard method of obtaining a fix. Personally, I made my own artificial horizon with an old 6-inches bathroom mirror, properly leveled using a precision surveyor level, accurate to 2 seconds of arc.

AstronavXls, version 12.8

Correction of a bug associated with the click box for meridian passage sights.
Two new converter tools were added in the Sight data sheets: a converter from the longitude difference between two meridians to the equivalent time difference in the sun passage, and the reciprocal, a converter from the difference in the sun time passage between two meridians to the equivalent difference in longitude.
Paul

AstronavXls, version 12.7

Fix of a minor problem occuring in the display of the GHAy projection label, in the time diagram of each "Sight" sheet (the South pole view), whenever the sight type (star, sun, planet or moon) was changed.
Paul

AstronavXls version 12.6

Since AstronavXls plots true circles of position (COP) rather than lines of position (LOP), all reference to LOPs have been modified to COP, except for the name of the plot sheet "LOP Plot" which has been preserved because its is used as a reference marker in the macro commands. I had kept the LOP identification because people are more familiar with the term, but it creates confusion. The equations used to perform the astronomical calculations or the various corrections have been added on the "Sight" sheets, either in a display box, or as comments attached to the appropriate description cells. Some minor bugs or errors have been corrected.
Paul

AstronavXls version 12.5

A new block (blue) entitled "Case of Latitude by Polaris Sight", has been added in the 3 "Sight input data sheets". As indicated by the title, this block is activated and shows the Latitude calculation and the azimuth angle results, whenever the name of the "Observed celestial body" is identified as "Polaris". The equation for the correction caused by the offset of Polaris with respect to the North Pole is indicated in the block. More details are given in the updated "AstronavXls user's manual". New Temperature converter (°F to °C) and Pressure converter (in of Hg to millibars) were added in the "Utilities section".
Paul