NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Latitudes by lunar distance. was: Lunars with and without altitudes
From: Dave Walden
Date: 2006 Nov 26, 14:23 -0800
From: Dave Walden
Date: 2006 Nov 26, 14:23 -0800
Apologies for the lack of documentation in the code. Like many/most engineers and scientists, I find the work fun, the report writing less so. I realized that if I didn't "just send it", I'd probably move on and never come back to write it up more properly. So again, apologies, and I'm more than happy to provide any answers/help/additional details people would find interesting. The previous post is a place to start on Maxima documentation. A reference I find useful is Michael Clarkson, DOE-Maxima Reference Manual, ver5.9, Aug 2002. (Try google for macref.pdf) %i10 is the usual equation for cleared lunar distance (Cotter p212 bottom following "From which:") I actually took it, with the fairly widely used notation, from, "Josef de Mendoza y Rios", Recherches sur les principaux Problemes de l'Astronomie Nautique, p79, as discussed earlier. In FORTRAN (and radians): D=acos( (cos(d)-sin(a)*sin(h))*(cos(A)(cos(H))/(cos(a)*cos(h))+sin(A)*sin(H)) Where, D is cleared distance, d is observed, a is apparent moon altitude, A is true moon alt, h is apparent star/sun/planet altitude, H is apparent star alt. Using the Nautical Almanac algorithm for position from intercept and azimuth by calculation p282, I get W69-33, N38-40. I purposely used Nautical Almanac precision. I will repeat with ephemeris values. On SD, I may have mistakenly used 16.2 for one star and 16.1 for the other. I meant 16.1. This is the Nautical Almanac value. It agrees to the nearest 0.1' for 30 to 60 degrees to the more precise value in this case. Again, more precision is possible. On refraction, that is indeed the method I used. I stopped at one term because it gave accuracy consistent with other choices. On parallax, yes the issue is the "backwards" correction. See for example, John Brinkley, Elements of Astronomy, 1819, pg 319. (Google books, full text) On earth shape, yes I neglected it for this calculation. Could be easily added. Next topic, eliminate need for AP. Approach, solve for equation of cone in space on which observed lunar distance is found. Find intersection of cone with sphere (earth) ((or flattened sphere)). Repeat for second cone/star. Intersection of two lines on sphere is position. (Unless one or both stars are very close to the moon, there will only be one such intersection.) I think I'm still a few days away. Anyone done it? Sorry, what computer "basic" matter? --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---