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Re: My first Lunar
From: Kent Nordstr�m
Date: 2008 Aug 4, 17:41 +0200
From: Kent Nordstr�m
Date: 2008 Aug 4, 17:41 +0200
Frank wrote [5988]: You found deviations as large as 0.6 minutes or arc in the clearing with a standard deviation of 0.3 minutes. That's a lot! Though I certainly can't guarantee it, I believe that my clearing results are accurate to 0.05 minutes of arc so I would say that you still have some things to fix. Even in the year 1790, a discrepancy of 0.6 minutes of arc in clearing a lunar would have been counted as "too large" except as a rough approximation. The results from my test cases with my input data into Frank's prediction model [5932] were as in columns 2-3 below. All data 1-8 are in minutes of arc directly read out from Frank's model. I still claim that my own LD prediction model is rather precise well aware of that I use old-fashioned methods. My results with the same input data, except for Jeremy's first lunar - case 8, as per above in my own model give errors in LD as per column 4. Column 5 is just a conversion to compare figures in arc min with what I got from Frank's model. So the relevant comparison is between column 2 and 5 : Case Frank's error in LD Frank's error in longitude My error in LD In arc sec My error in LD in arc min 1 0' 1' -5,5" -0,092' 2 0,6' 19' -2,1" -0,035' 3 -0,3' 10,3' 5,5" 0,092' 4 0,3' 9,6' -1,5" -0,025' 5 0,1' 3,3' 0,06" 0,001' 6 -0,2' 5,5' -2,3" -0,038' 7 0,4' 11,1' -0,5" -0,008' 8 0,1' 1,8' - - Mean 0,125' 7,7' -0,91" -0,015' Std. Dev. 0,3' 6,0' 3,3" 0,055' Frank's comment that an error of 0,6' was to large in 1790 can be questioned. I would say that navigators then were likely not unhappy to find longitude within 15-20 M (0,5-0,7 min of arc in LD). The errors in my LD's are referred to test cases taken from text books. You can of course always ask what is correct. Kent N ----- Original Message ----- From:To: Sent: Sunday, August 03, 2008 3:02 AM Subject: [NavList 5988] Re: My first Lunar > > Kent, you wrote: > "I have now made a comparison between Frank's model and mine and here are > the results. In all cases I have used my own way to compensate for > oblateness/flattening. By using my data in Frank's modell error in lunar > and > and error in longitude are read out. > [...] > So it seems to me that my model is rather good. The deviations are > probably > that I model e.g. refraction and oblateness/flatness in a different way > from > Frank." > > You found deviations as large as 0.6 minutes or arc in the clearing with a > standard deviation of 0.3 minutes. That's a lot! Though I certainly can't > guarantee it, I believe that my clearing results are accurate to 0.05 > minutes of arc so I would say that you still have some things to fix. Even > in the year 1790, a discrepancy of 0.6 minutes of arc in clearing a lunar > would have been counted as "too large" except as a rough approximation. > > -FER > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---