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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Saturn Lunar by DSLR Camera
From: Antoine Couëtte
Date: 2017 Sep 30, 03:30 -0700

re : Rudzinski-sep-2017-g40199 and Couëtte-sep-2017-g40210

Hello Greg,

I have been reworking your recent Saturn Lunar with http://reednavigation.com/lunars/lunars_v4.html through successive iterations as described in Couëtte-sep-2017-g40210 :

1 st result

From your Distance = 2°36.4' , get Error in Lunar -0.2', Approximate Error in Longitude 5.1' , translating more accurately into Error in Lunar = -10.2".

Let's remove this error, i.e. subtract (-10.2") from our initial 2°35.4' distance and run the whole computation again.

Note : For the upcoming successive iterations only the sextant distance itself needs to be corrected onto http://reednavigation.com/lunars/lunars_v4.html :

2 nd result

Starting with 2°36.4' - (- 10.2") = 2°36.570', get : Error in Lunar 0' (no sign given here), Approximate Error in Longitude 01.1', translating more accurately into Error in Lunar = +/- 2.2 " (since no sign given earlier). Let us assume that the " - " sign is still the correct one.

3 rd result

Starting again from 2°36.570' - (-2.2") = 2°36.610' , get : Error in Lunar 0', Approximate Errtor in Longitude 0.2', translating more accurately into Error in Lunar = +/- 0.4" .

Let's continue keeping the " - " sign and start from 2°36.610' - (-0.4")  = 2°36.617' . We finally obtain :Error in Lunar 0', Approximate Error in Longitude 0.0' .

Bingo ! :-)

Discussion :

1 - The final result of http://reednavigation.com/lunars/lunars_v4.html obtained through 2 iterations is : 2°36.617' . It is 0.217' distant from your early value of 2°36.4'. Therefore the initially displayed " Error in Lunar -0.2' " statement is 100% right.

2 - This most recent Saturn Lunar of yours is a good example of a short distance Lunar - less than 3° - where http://reednavigation.com/lunars/lunars_v4.html immediately yields the right result. On the other hand for the recent Regulus occultation ( Couëtte-sep-2017-g40210 ) its first displayed result ( -0.8' Error at sea level ) - was off by 2.2' and totally unreliable. The actual value was slightly over 3.0' as also independently confirmed in Hirose-sep-2017-g40222 until now. Eleven subsequent manual iterations - of the kind demonstrated here-above - ran onto http://reednavigation.com/lunars/lunars_v4.html yielded a final result within of few arc seconds of the results listed in Hirose-sep-2017-g40222 .

3 - Last but not least, this systematic iteration method - although not necessary for this specific short distance Saturn Lunar - is an excellent and easy way to get the most out of http://reednavigation.com/lunars/lunars_v4.html . Let's us simply hope that it can be simply implemented in "automatic mode" through limited software modification to the currently existing v4 version.

Frank - who must be overloaded day and night with the preparation of his upcoming NavList Symposium - hopefully will have time to look into it in some near future.

Thanks to all for your Kind Attention, to you Greg especially for your on-going excellent contributions. And also :

Warmest thanks in advance to you Frank, if you can find time to "upgrade" http://reednavigation.com/lunars/lunars_v4.html which - again - is already a fabulous tool you invented for our greatest satisfaction and interest.

Kermit

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