# NavList:

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

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Re: Latitude by Lunar Distance
From: Frank Reed CT
Date: 2006 Nov 12, 00:21 EST
George H wrote:
"Finally, Frank has been asked to explain a procedure for deducing
observer's position from two Moon-star distances, quoting numbers.
Even a contrived, fictitious example would be worthwhile. "

Sigh... I feel that I have done this, George. The required information is in NavList messages 1366 and 1379. You can read them here:
(note the column of message numbers on the right --you can sort the messages by clicking on the up/down arrows).
If you need more explanation, then please explain what you're looking for.

"Is it necessary to presume an approximate observer's position beforehand?"

Yes. But no more so than in a traditional Sumner line situation.

One way to organize the setup for drawing the lines of position: take the DR lat, lon, and then look at four points around it in a square (let's say a degree on a side). Clear the lunar at each point. This gives you an "error" in the lunar at each corner. Interpolate along the sides of the square to find the points where the error would be zero. That gives you two points and thus one LOP. Repeat for the second body. Cross the LOPs. That's your fix. Does that help you see it better? Note that this is merely one way to organize the plotting of the LOPs. By the way, consider drawing "dotted" lines parallel to each LOP on either side, where the error would be 0.1 minutes of arc. That's a nice graphic representation of the potential error for the observations in question (where the cone of position intersects the Earth's surface at a shallow angle, the band between the dotted lines will be wide).

-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars

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