A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ed Popko
Date: 2016 Aug 27, 17:11 -0700
After some really awful weeks of hot humid weather, we are getting slight hints of cool and clear sky Fall weather. This plus the recent waning moons (ages 21-25) have revived my interest in taking morning lunars.
A really big help is having an approximate pre-set for the sextant for near-limb lunar shots. Some might say this is cheating - Ed needs to practice bringing it together. But I'm not of that kind. Consider that 19th c lunarians had almanacs with lunar distances listed for every three hours of the day and surley they had some sense, even an hour off, of what GMT was so they are doing what I want to do.
I have a calculator program that tries to find the limb-to-limb sun-moon distance given the GHA/Dec/SD of both. Curently, I'm using standard formulas for finding the geo-centric distance (arc) between them and then, I subtract the moon and sun's SDs. The reslt is the pre-set.
Most of the time, this gets both bodies in the telescope's field which is a good start. But depending on the height of the bodies, sometimes the images are superimposed, other times separated etc.
So.. I'm looking for an improved way to compute the pre-set. There is no point in reverse engineering any of the lunars reduction methods. I don't need precision, just good dependable starting angle. Also, I do not want to consider heights of bodies, I usually work from an open field in the Catskill Mountains and there are no convenient horrizon and besides, Frank's lovely lunars web calculator doesn't need heights anyway).
Any suggestions are appreciated.