A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Jim Rives
Date: 2020 Jan 12, 17:09 -0800
I am following the process outlined in an article you wrote on April 27, 2004, "Lunars Are Easy". I have searched for that title on NavList from 2003 on but can't find it again. In any case, I was doing fine through "Calculateing the Geocentric Lunars"... 85d 08.8' agreed exactly with your Lunars app. Then the fun began when I tried dealing with Stellarium. You pointed out in a recent post that it shows altitudes without dip and with refraction and parallax to the center of the object, the sun and the moon in this case.
I think the weirdness creeps in "Altitude Correctons from the Almanac". I'm using a 2020 almanac, but I imagine it hasn't changed much for this refraction data over the past 14 years, right? Basically " to complete the clearing process, we need accurate values for dh_Moon and dh_Sun. These are the combiined effects of parallax and refraction." Then, "opening the front cover of the Nautical Alamanc, the altitude correction for the Sun at 47 degrees altitude is -0.8 minutes." In the Apr.-Sept column for 47d I get LL and UL corrections of +15.1 and -16.6, respectively. I can't see how we get to -0.8.
For the moon it is even weirder (as usual). The basic correction for 46.7d altitude is 49.3' and additional corrections for LL and UL are, for an HP of 54.7, about 2.1 and 2.4 or so, both positive. And the UL has to have the resulting correction reduced by 30.0'. Resulting in a correction of 36.5. I cannot see how to get there.
But... I am fairly confident that the shooting itself was ok. I think this may have been easier if I actually took altitudes for the sun and the moon, but there was no horizon. I'd love to be able to use Stellarium, or some other tool, to get the altitudes so I can mess with this frequently and actually get fluent it the methods. But for this particular shoot I am hung up at this point.
Moon is in distance again on the 17th! Only 5 days to go!