NavList:

re : http://fer3.com/arc/m2.aspx/Longitude-calculator-theodolite-Pennino-jun-2013-g24454

Hello Bruce,

Thanks for publishing your theodolite data which I first decided to "number-crunch" them as standard LOP's.

Here are the starting data I have used under our " CelNav classical form", as "best-guess processed/derived/translated" from the ones you published :

UT Date of observations : June 20th, 2013 around 00h30m00.0s UT1
TT-UT = +68.3s

Observer's Position at N42°2°'3 W071°48'5 and Altitude : 241m above WGS84 Ellipsoid (as per Google Earth)

HOE = Oft *** P = 990mb = 29.23"Hg *** T = 20°C = 68°F

UT = 00h27m02.0s Zenith Distance = 59°53'44" Height = 30°06'16" i=+0.1 NM Z = 163.6°

UT = 00h28m36.0s Zenith Distance = 59°48'51" Height = 30°11'09" i=+0.5 NM Z = 164.0°

UT = 00h30m23.0s Zenith Distance = 59°43'54" Height = 30°16'06" i=+0.5 NM Z = 164.5°

UT = 00h31m35.0s Zenith Distance = 59°40'30" Height = 30°19'30" i=+0.6 NM Z = 164.8°

UT = 00h32m26.0s Zenith Distance = 59°38'27" Height = 30°21'33" i=+0.4 NM Z = 165.0°

I am using own internal Moon Ephemeris believed to be accurate to +/- 4".

I am not absolutely sure that I have correctly "translated" your data into our usual CelNav form. Please be so kind as to confirm this point, and if not please indicate which such "translated data" should be, and how you derive them from the ones you did publish.

Anyway, from what I can see all your intercepts are below 1 NM, which already fully confirms Frank's predictions.

And assuming that my "data transcription" is correct, these intercepts would tend to indicate suspecting an instrument zero offset.

I fail to see the interest of deriving your Longitude from your known Latitude, with such observations so close from the south. Would they be much closer to West or East they would be definitely better in this regard.

If you do want to compute Longitude from Latitude from these "rather south" observations, which exact Formula are you using ?

I am asking simply because our standard CelNav Formula "sin(Height)=sin(Lat)*sin(Dec) + cos(Lat)*cos(Dec)*cos(Body Local Hour Angle)"
is not best suited to determine "Body Local Hour Angle" as its cosine starts becoming close from 1, as is the case here.

Any comments will be highly appreciated, from yourself or from somebody else well familiar with theodolite observations.

Standing by, and many thanks in advance

:-)

Best Regards from

Kermit

PS : Many moons back - in the early 90's - , I performed theodolite observations to determine our Home position through standard brute force LOP's , and - from some 100 observations from SUN, Polaris, and some selected stars - I was able to eventually narrow it down with an error a little less than 2", i.e just within 50 meters from the coordinates currently indicated by Google Earth. I happen to be lucky at times.

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