A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2010 Dec 29, 12:36 -0800
If you want the most precision in advancing the LOPs mathematically then you can compute the Motion Of the Observer (MOO) correction on your calculator. First you calculate the relative bearing to the star by subtracting course (or "track" in flight practice) from the azimuth of the body. The table I posted:
limits the relative bearing to the range of 0 to 180, from straight ahead to straight behind on either side of the vessel but, when using a calculator, you can use any relative bearing from +360 to - 360 since the calculator will come up with the correct sign for the cosine so the result will have the correct sign for applying the correction to the Ho. So to calculate relative bearing just subtract course from azimuth: RB=Zn - C.
Then you take the cosine of the RB and multiply by the speed in knots (which would give you the correction for a one hour time period,) divide by 60 to find the correction per minute and then multiply by the time you are advancing the LOP, the number of minutes and fractions of a minute. (If you want to work with seconds of time, divide the speed by 3600 and then multiply by the number of seconds to advance the LOP.)
So the complete formula to find the correction in minutes of arc is:
MOO = cos (Zn - C) * speed /60 * time.
--- On Wed, 12/29/10, Gary LaPook <glapook---.net> wrote: