NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Andrés Ruiz
Date: 2009 Oct 1, 11:53 +0200
My solution:
Peter,
if I have not done
anything wrong, the possible difference could come from this:
Jim Wilson correction for
time depends on latitude, B:
Dt = 3600.0*180.0/PI *
(dBdt - dDecdt) * (TAN( B ) - TAN( Dec )) / SQ( dLHAdt )
In this case, high N/S component of the velocity,
the difference between the time of maximum altitude and LAN is very important,
and also the associated altitude.
If you take estimation
for latitude using the Hmax, de solution becomes erroneous.
Andrés Ruiz
Navigational Algorithms
http://sites.google.com/site/navigationalalgorithms/
De: navlist@fer3.com
[mailto:navlist@fer3.com] En nombre
de P H
Enviado el: jueves, 01 de octubre
de 2009 8:20
Para: navlist@fer3.com
Asunto: [NavList 10012] Re: Time
of meridian passage accuracy
UT of LAN:
17:17:35
Latitude at LAN:
N 22 deg 40.8'
Longitude at LAN:
W 79 deg 42.4'
Peter Hakel
From: Gary
LaPook <glapook@pacbell.net>
To: navlist@fer3.com
Sent: Wednesday, September 30,
2009 9:19:19 PM
Subject: [NavList 10009] Re: Time
of meridian passage accuracy
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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