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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Reality check
From: Frank Reed CT
Date: 2006 Jun 6, 02:24 EDT
From: Frank Reed CT
Date: 2006 Jun 6, 02:24 EDT
Guy asked: "When using HO 249 The assumed latitude is rounded and the assumed Longitude is the number that will make the LHA an even number (within the range of +/- 30 min. of the DR Longitude). When plotting the assumed Lat and Long are used as the starting point of the procedure. OK if I use the formulas: Sin-1Hc = sin(dec) x sin(lat) + cos(dec) x cos(lat) x cos(LHA) and Cos-1 (Zn)= sin(dec) - sin(lat) x sin(Hc) / cos(Hc) x cos(lat) to calculate Hc and Z or Zn and then plot my position wouldn't I be using the DR position as the start point?" Right. Those tables require a "contrived" AP for each sight in order to get to integral values for the table look-ups. When you're using the direct equations, you can just use your DR. This generally results in much shorter intercepts which are usually easier to plot. Some other tabular methods, for example HO 211, also let you work from the DR position. The cost is more calculational work and more room for error. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars
