A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Mark Coady
Date: 2015 Oct 21, 12:45 -0700
A special thank you to Frank Reed for a wonderful Lunar course this last weekend. It was informative and interesting, and I learned alternative solution methods and developed a better understanding of the subject.
When I first started learning Lunars on my own, I wandered the internet searching for understandable (a key point) descriptions of technique. I found some interesting variations I revisit now with better understanding.
I was curious if anyone has particular experience or comment with the method I will briefly describe that is more fully presented in the following article:
Longitude by the Method of Lunar Distance by Wendel Brunner, PHD, MD Mar 21, 2005
The methods I have considered to date take an observed distance and altitudes and calculate a “true” or corrected Lunar distance. This then is compared to a pre-calculated or nautical almanac calculated reference bracket for interpolation. Some methods are far less cumbersome than others if using logarithms. Then, with already taken nearly simultaneous altitudes of moon and sun, you have data at hand to use to calculate crossing LOP’s using your newly verified/corrected clock time.
Brunner’s method is an interesting curveball. He works a bit backwards from the aforementioned pattern. In his method we:
Record an observed lunar distance and an altitude of a handy body, most likely, but not required to be the moon or sun.
Use your assumed GMT, your altitude sight, your DR or known latitude and calculate your assumed longitude.
Use the resulting position/almanac and calculate what should be the “observed” (not corrected) Lunar distance for that positon through the law of cosines, and manipulation of other corrections, etc. Adjust your position using the calculated difference between the taken sextant “observed” and calculated “observed” position.
Reiterate the calculation process using the adjusted/corrected GMT and longitude, until deviation between the taken and calculated “observed” is within your accepted tolerance.
The result ends up with a corrected GMT and Longitude.
My thoughts lead me to it being an interesting diversion, but a bit cumbersome without a computer program. Neither the spherical trig equations or multiple pass iterations are fun with logarithms, so it quickly falls at the least to a calculator method. He alludes to the fact that he has calculator programmed to do essentially everything including the iterations. Obviosly a programmed calculator can reiterate happily without pain.
Has anyone else played with this before? If so..where there any revelations? I suppose if I had just grabbed an LD between clouds, with no altitudes possible..then I would use my DR positon for calcualted latitudes, etc.........
Barring that the method lacks any immediate enchantment on inspection....