A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2019 Dec 22, 13:37 -0800
Mike Freeman you wrote: I note using AP3270 vol 1 when you plot your LOP's and decide on your fix your work is not yet done. There is the matter of precession and nutation in table 5.
Don’t get stressed out over correcting for P&N. There’s really very little to it. Cunliffe only donates a paragraph to it, so he doesn’t go into detail over how to apply it. You don’t need to move the actual LoPs themselves. Like he says, if all the bodies are from Vol 1, you can just move the fix by the appropriate amount once you’ve plotted it. If not all the bodies are from Vol 1, e.g. you might have a planet amongst them, just move the assumed positions of the bodies from Vol 1 by an amount equal to N&P before you plot the LoPs from them. This idea of moving the assumed position can be used at any time when the book says move the LoP. It might be to apply MOO if your pre-computing’s gone out of the window, or Corioli’s acceleration if you’re an air navigator. It saves getting a confusing lattice of lines all over your chart. One thing I've found is that it’s difficult to set tiny distances accurately on many types of dividers. It’s sometimes easier to mark in mm from a ruler, which is another reason for using a fixed and convenient latitude scale on a plotting sheet if you use one. DaveP