Author

Topic: NAO/Long Term Almanac vs N(x) Sight Reduction Discrepancies

bterhart

posted March 12, 2018 12:38 PM
Hi,
In working through some practice problems, I've come across an example sight reduction in Kolbe's Long Term Almanac that I can't reconcile with the N(x) tables as published in Celestial Navigation: A Complete Home Study Course 2nd Edition
On Page 72 of Kolbe, observational data for Dubhe yields an Hc and Zn of 36 54 and 327.2 respectively. I can reproduce these results via calculator.
Using the N(x) tables with this observational data, I get wildly different result even with very careful interpolation. In reducing other practice sights, the N(x) tables have always produced accurate results.
I must be doing something wrong, but for the life of me I can't figure it out.
Here's my N(x) reduction: GHA Dubhe (given): 118 47 Dec Dubhe (given): N61 33 DR Lat (given): 55 15N DR Long (given): 2 43 W
LHA=GHAWestLong=118 47  2 43 = 116 04 Assumed Long= 2 47, LHA therefore 116 Assumed Lat = 55N
N(v) = N(90Dec) + N(t) where t = 116 as LHA < 180 as t > 90, t=180LHA=180116=64 N(v) = N(90  61.55) + N(64) N(v) = N(28.45) + N(64) N(v) = 741.5 + 107 N(v) = 848.5 v = 25.34
N(w) = N(Dec)  N(90v) N(w) = N(61.55)  N(9025.34) N(w) = N(61.55) N(64.66) N(w) = 128.5  101.5 N(w) = 27 w = 76.7
u = 90  w + Lat (Dec N and DR N, therefore same name, therefore + Lat) u = 90  76.7 + 55 u = 68.3
N(Hc) = N(90  v) + N(u) N(Hc) = N(90  25.34) + N(68.3) N(Hc) = N(64.66) + N(68.3) N(Hc) = 101.5 + 74 N(Hc) = 175.5 Hc = 57.05 Hc = 57 03
The N(x) derived Hc of 57 03 is wildly different than the 36 54 given in Kolbe (and calculator sight reduction). What am I missing? Where's the error in my N(x) calculation or assumptions?
TIA Bert
From: Nanaimo


David Burch

posted March 12, 2018 03:51 PM
Please look over these answers to see if that helps.
From: Starpath, Seattle, WA


bterhart

posted March 12, 2018 04:31 PM
Hi David,
Got it! Much appreciated David! I didn't make the translation when original t > 90 such that w = 180 w. Looking through the explanations in the CelNav book, I don't find that note. Is it missing? Did I miss it?
Lastly, is there a link for the N(x) table checker that you're using?
Thanks again David : )
Bert
From: Nanaimo


David Burch

posted March 12, 2018 04:52 PM
This should be on table T27, page 270 in the latest printing of that book. It is on the Emergency Card.
No that is not public that i know of, but I have on the list to do a short article on the N(x) solution and will double check it and make a link to it at that time. Also need to check with the author of the that utility.
Should be in about two weeks we can get to that. If that does not appear in our blog by then, please post a reminder
www.starpath.com/articles
From: Starpath, Seattle, WA


bterhart

posted March 12, 2018 11:14 PM
Hi Dave,
I've got the eBook version and there's nothing in the T27 that references the modification to w if original t > 90.
I'll look forward to the upcoming article...
Thanks Bert
From: Nanaimo


David Burch

posted March 13, 2018 10:26 AM
May I ask what format of ebook do you have and when did you purchase it?
This was updated at some point, but i do not recall when.
From: Starpath, Seattle, WA


bterhart

posted March 14, 2018 10:24 AM
Hi Dave,
I purchased a Kindle edition of the book May 31, 2016 from Amazon (along with the Radar, Inland and Coastal Nav, Starfinder, Modern Weather, and Emergency Nav).
Thanks, Bert
From: Nanaimo


bterhart

posted April 05, 2018 05:37 PM
Hi Dave,
Here's that two week reminder you asked for...
Thanks, Bert
From: Nanaimo


David Burch

posted April 05, 2018 06:24 PM
We are just at the last stage of finishing a new book so i cannot get to this for a bit longer, but i will write to the author of that app to see if it can be distributed. I think it can, maybe already has, but we have to check.
From: Starpath, Seattle, WA


bterhart

posted April 05, 2018 06:41 PM
Thanks for the update Dave : )
From: Nanaimo


David Burch

posted April 06, 2018 11:32 AM
I have contacted the author of that app, Stan Klein, and he is making a version we can distribute.
Thanks for motivating this work. I had almost forgotten that we had this valuable tool for learning the N(x) table.
From: Starpath, Seattle, WA


