A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Frank Reed
Date: 2017 Dec 4, 15:40 -0800
Chris, you wrote:
"My assumed position is actually where I am at, so with the actual LHA being so close to an integer, I expected the intercept to be closer. Are there other things in Pub 229 other than the LHA that affect it's accuracy, or am I missing a concept?"
Yes, I think you're missing a concept. Tables like 229 and 249 require you to pick a very specific assumed position. Setting aside the LHA aspect for now, 229 requires an AP that is an integer latitude, too. Your location, which I believe is Burlington in Vermont, happens to be around 44.48°N, just about halfway from 44° to 45°. When you work a sight with 229, your AP will be on one of those integer latitudes, which implies that your intercepts in Burlington could easily be 30 nautical miles in length, depending on the azimuth of the body and other issues. Despite their length, those intercepts will produce generally accurate lines of position, but this won't be obvious until you plot them. It's counter-intuitive, and that's one of many reasons that I try to persuade folks not to use those tables unless they have to or they really want to replicate navigation from the "disco era".