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

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Re: Moon Venus Lunar - Interpretation of results
From: Jim Rives
Date: 2020 Jan 31, 17:38 -0800

Sean, you wrote:

"No. The error in your *measurement* was 16'. Under the circumstances, this would cause an error in time of 32 minutes and 3 seconds - giving a "measured time" of 21:37:57. That is an error of 1,923 seconds. Divide that by four and you get 480.75 arc minutes or 8°00.8'."

And

"Take the error in longitude in minutes (in this case 8° · 60  = 480 + 00.8' = 480.8') and multiply by 4 (480.8 · 4 = 1923.2). That is the error in seconds of time. You can divide that by 60 to get the decimal minutes (1923.2 / 60 = 32.0533...) and multiply the mantissa by 60 to get the seconds - or you can divide the error in seconds by 3600 to get decimal hours and, if you're using a calculator that can dislay in DMS format, get the minutes and seconds directly."

I was not aware that the lunar cycle was 12d/day and that the lunar error referred to that arc. So, it seems that my Error in Lunar from Frank's app, expressed in arc-minutes along the lunar path, should be multipied by 2 to get to elapsed time in minutes.  Then use that time and calculate the difference in expected and observed GMT using the sun's rate of travel, and use that for the longitude.  Is this on the right track?   I just worked it on my corrected lunar from last night and it agreed with Frank's app.

BTW, Frank looked at my wacko looking results and noted that I had used an old LD lying carelessly around on the spreadsheet. The observed lunar distance I should have used was  15d 38.3.  With the correct one the Error in Lunar was '1.

I immediately recognized the lunar method you used from Frank's Easy Lunars.  Last month I made it a project to carefully work by hand each of the three methods he gave in the Lunars class.  I have gotten two of them done, and I recognized intermediate variables A, B, and Q.  Is the output from an excel worksheet or other program?  Or did you just work that out with a calculator on the fly?  Either way, it is a very helpful summary of the method.  I have gotten reacquainted with my old Staedtler white erasers!

Jim

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