NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A practice round of stars
From: Peter Hakel
Date: 2013 Mar 2, 10:03 -0800
From: Greg Rudzinski <gregrudzinski@yahoo.com>
To: pmh099@yahoo.com
Sent: Saturday, March 2, 2013 10:34 AM
Subject: [NavList 22577] Re: A practice round of stars
Greg Rudzinski
[NavList] Re: A practice round of stars
From: Jeremy C
Date: 2 Mar 2013 06:18
Hmmm, While I agree with your Longitude Stan, I can't say the same for Latitude. You are off both by my calculated position and GPS. So either there is an error in your math, or I mis-typed something.
From: Peter Hakel
Date: 2013 Mar 2, 10:03 -0800
Jeremy,
I checked the numbers (ephemerides, Hc's, azimuths, intercepts, etc.) from my spreadsheets against the USNO website and the Navimatics "Celestial" iPhone app. They all agree except for a couple of places, which differ by 0.1' (Moon SD -> Hc -> intercept; Rigel intercept).
The final step in my case is the many_body_fix.xls spreadsheet that uses the least-squares-based computation procedure described in the Nautical Almanac Commercial Edition, which also includes vessel motion. When I zero out the vessel speed in that spreadsheet, I exactly recover the fix given by the "Celestial" iPhone app:
Lat: N 8d 50.0'
Lon: E 109d 45.3'
I checked the numbers (ephemerides, Hc's, azimuths, intercepts, etc.) from my spreadsheets against the USNO website and the Navimatics "Celestial" iPhone app. They all agree except for a couple of places, which differ by 0.1' (Moon SD -> Hc -> intercept; Rigel intercept).
The final step in my case is the many_body_fix.xls spreadsheet that uses the least-squares-based computation procedure described in the Nautical Almanac Commercial Edition, which also includes vessel motion. When I zero out the vessel speed in that spreadsheet, I exactly recover the fix given by the "Celestial" iPhone app:
Lat: N 8d 50.0'
Lon: E 109d 45.3'
So, with vessel motion, at 1900, I still get:
Lat: N 8d 49.0'
Lon: E 109d 45.2'
Evidently the
longitude is less sensitive to this detail compared to the latitude; that is to be expected given the ship's course (037).
It is always possible to compute some numbers, which is why I also did the detailed plot on the metric graph paper as an independent check. I was happy with what I got, but now I wonder if I'm missing something.
Peter Hakel
PS. Just to be sure - since the index error is ON the arc, I have been SUBTRACTING 0.9' from all sextant altitudes in the alt_corr.xls spreadsheet. Now, the app asks for "IE", which I enter as positive, but the value is then displayed also as positive in the CORR field of the app, even though the result (Ho) agrees with my subtraction…
PPS. After seeing the two messages from Greg, I have to say that I never saw any postings from Stan, so I assumed that Jeremy was responding to me.
Peter Hakel
PS. Just to be sure - since the index error is ON the arc, I have been SUBTRACTING 0.9' from all sextant altitudes in the alt_corr.xls spreadsheet. Now, the app asks for "IE", which I enter as positive, but the value is then displayed also as positive in the CORR field of the app, even though the result (Ho) agrees with my subtraction…
PPS. After seeing the two messages from Greg, I have to say that I never saw any postings from Stan, so I assumed that Jeremy was responding to me.
From: Greg Rudzinski <gregrudzinski@yahoo.com>
To: pmh099@yahoo.com
Sent: Saturday, March 2, 2013 10:34 AM
Subject: [NavList 22577] Re: A practice round of stars
Stan didn't put a time to his position which looks to be near Peters 1900.
Greg Rudzinski
[NavList] Re: A practice round of stars
From: Jeremy C
Date: 2 Mar 2013 06:18
Hmmm, While I agree with your Longitude Stan, I can't say the same for Latitude. You are off both by my calculated position and GPS. So either there is an error in your math, or I mis-typed something.
How are you reducing it? By tables and chart, computer, slide rule, formula?
Jeremy
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