A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2017 Nov 3, 04:51 -0700
Nov 03 rd, 2017
1 - It looks like the data published by Ron Jones pertain to Stars geocentric Altitudes, i.e. obtained through correcting the topocentric altitudes for sextant error, dip, refraction, semi-diameter and parallax.
For the Stars once sextant error corrections have been performed (unknown here, so let’s assume them equal to zero in this example) the only appreciable corrections are dip (unknown here, so let’s again assume them equal to zero), and refraction.
Most likely your Ti-89 Starpilot software expects topocentric altitudes corrected for only sextant error, and NOT geocentric altitudes.
Hence if you want to use your TI-89 Starpilot Software to its best accuracy, then you should “reverse engineer” Ron’s published heights in order to transform them from geocentric into topocentric ones.
From a Nautical Almanac Refraction Table, e.g. French Ephémérides Nautiques TABLE I : Réfractions Astronomiques moyennes (760 mm Hg, +10°C) standard refraction table, get the following results through “reverse engineering” Ron's published geocentric altitudes as follows :
- for H geocentric = 26°01.81’ , get Sextant corrected topocentric altitude = 26°03.78’
- for H geocentric = 14°46.68’ , get Sextant corrected topocentric altitude = 14°50.30’
- for H geocentric = 15°45.66’ , get Sextant corrected topocentric altitude = 15°49.05’
It you now enter your TI-89 Starpilot Software with such “reverse engineered heights”, for height of eye = 0 m (no dip) you will very likely find end results quite close from the ones subsequently published by Ron Jones as being S07°57.0’ - W014°20.9’.
2 - You are asking (here-under) what kind of results some others had got through their calculators.
2.1 - When treating Ron’s data as geocentric heights, I am getting for Mirfak / Canopus / Peacock his exact published fix value, i.e. S07°57.0’ - W014°20.9’ . When running all the stars from this fix, I am getting every single time : Intercept = 0.0 NM (meaning that it is smaller than 0.05’), and for the full stars only series, I am getting S07°57.002’ and W014°20.900’.
This is a confirmation that Ron’s published values are geocentric. In other words, these are already fully corrected heights.
2.2 - If - by mistake - I consider instead that the values published by Ron were topocentric and corrected only for sextant error, with only Mirfak, Canopus and Peacock I am getting the following fix : S07°54.9’ - W014°23.1’, i.e. quite close from your value given here-under ( " new fix = 7°54,9’S 14°23’3W " )
2.3 - From the reverse engineered heights here above with only Mirfak, Canopus and Peacock I am getting the following fix : S07°57.04’ - W14°20.95’ which is extremely close from Ron’s published solution.
This is a second confirmation that you should rework your TI-89 Starpilot program with the reverse engineered heights given here-above. Please be so kind as to indicate your results.
Re: Where in the world am I (RE : http://fer3.com/arc/m2.aspx/Where-world-am-I-Dekker-oct-2017-g40491)
From: Herman Dekker
Date: 2017 Oct 26, 01:23 -0700
Solved the problem as follows.
I took 3 stars arbitrary Mirfak, Canopus, Peacock (could not find triad with 120° separation).
Typed the info of the 3 stars in TI-89 Starpilot with DR 0° 0° this resulted in a fix 7°59`S 15°04`W.
Redid the calculation of the stars with the fix as DR, new fix = 7°54’9 S 14°23’3 W
Well acceptable result for me.
Others who used there calculator for solving the fix?