# NavList:

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

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Re: Time of meridian passage accuracy
From: Gary LaPook
Date: 2009 Sep 30, 21:19 -0700
Jim Wilson wrote on Sept. 26th:

"I compiled a table in my Navigation paper showing differences between maximum alititude and meridian passage ranging from 10 seconds to 37 minutes. My trial which led me to write the paper had a difference of a minute and a half, and that was at a moderate latitude and sailboat speeds."

I am curious how well it works at higher speeds. I have created a data set and I would like you to evaluate it and tell me the time of meridian passage, the longitude and the latitude at meridian passage.

This hypothetical takes place on December 22, 2009 and the sights are taken at five minute intervals on the exact five minute mark and all sextant corrections have been applied so the values stated are the observed altitudes, Ho. They cover a two hour period from 1700 Z to 1900 Z.

17:00:00     42º 14'
:05         42º  44'
:10         43º  13'
:15         43º  39'
:20         44º  04'
:25         44º  26'
:30         44º  47'
:35         45º  06'
:40         45º  22'
:45         45º  36'
:50         45º  49'
:55         45º  59'

18:00:00    46º  06'
:05         46º  12'
:10         46º  15'
:15         46º  16'
:20         46º  14'
:25         46º  10'
:30         46º  04'
:35         45º  56'
:40         45º  45'
:45         45º  33'
:50         45º  18'
:55         45º  01'

19:00:00    44º  41'

The D.R. at 1700 Z is 24º  25' N, 79º  50' W.

The course is 180º True.

The ground speed is 300 knots.

gl

James N Wilson wrote:
Douglas:

You state that "the effect is very small as to be of no practical concern to practical navigators."

I compiled a table in my Navigation paper showing differences between maximum alititude and meridian passage ranging from 10 seconds to 37 minutes. My trial which led me to write the paper had a difference of a minute and a half, and that was at a moderate latitude and sailboat speeds.

Jim Wilson

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