# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Pub. 249 question
From: Ron Jones
Date: 2017 Nov 27, 12:08 -0800

Using the "Sight Planning" worksheet in my "Celestial Navigation" Excel workbook for a sight planning exercise on the evening of 18 May 2017 at Ediz Hook (Lat 48° 8.5' N  Lon 123° 26' W).

I found that the "best " stars for a 2 body fix are REGULUS & CAPELLA which produce LOP crossing angles of 87°and the "best"  stars for a 3 body fix  are DENEB, SPICA, & POLLUX  which produce an azimuth spread of 238° with LOP azimuth dispersion angles of approximately 120° between each the 3 LOPs .  (see attached "Ediz Hook 18 May 2017 Sight Planning.pdf")

My H.O. 249 Volume I (EPOCH 1975.0) for Lat = 48°N & GHA of Aries = 180° List the following seven stars:

@DENEB , VEGA, ARCTURUS, @SPICA, REGULUS, @POLLUX, CAPELLA  ... . all of which are magnitude 1 stars.   The stars suitable for a 3 body fix are designated  by the @ symbol.  Of the 41 stars used in Volume I of H.O. 249 ....  20 are above the horizon at Ediz Hook on Greenwich Date 19 May 2003 @ 04:28:24 GMT .    Question, was a manual process such, as  the one used by the "Sight Planning" worksheet in my "Celestial Navigation" Excel workbook, used to select the seven stars, or was an algorithm used?   I am interested in finding the algorithm used by Volume I HO 249 for star selection, if one exist.

To download the "Celestial Navigation" workbook go to https:\\uspsd16.org  & select "Dept Info" and from the drop down menu select "Educational" & under the "Quizzes | Workbooks | Software" section & click on "Celestial Navigation".

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