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Bill:
Thank you.
Your answer is the missing piece to my puzzle
I now added a test for sine of LHA >0
8-).
Guy
      Hc and Zn by calculation using casio fx 260 calculator
     Sin-1Hc = sin(dec) x sin(lat) + cos(dec) x cos(lat) x cos(LHA)

       sin(dec) x sin(lat) =
      A= 0.207883238 X 0.644790904 0.134041221
     cos(dec) x cos(lat) x cos(LHA) =
      B= 0.978153648 X 0.764359006 X 0.965389226 0.72178344
         Total A + B 0.855824661
      Declination,  +North -South  North Shift Sin-1(Hc)  58.85095947
      Latitude,  +North -South  North 0999 Hc 58? 51.1'

     Cos-1 (Zn)= sin(dec) - sin(lat) x sin(Hc) / cos(Hc) x cos(lat)
       cos(Hc) x cos(lat) =
      A= 0.517255471 X 0.764359006 0.395368878
       sin(lat) x sin(Hc) =
      B= 0.644790904 X 0.855831045 0.551832073
       sin(dec) - B =
      C= 0.207883238 - 0.551832073 -0.343948836
       C / A =
      D= -0.343948836 / 0.395368878 -0.869944134
         Shift Cos-1 (Zn) 150.4521481
         0999 Zn 209? 32.9'

----- Original Message -----
From: "Bill" 
To: 
Sent: Monday, May 29, 2006 4:00 PM
Subject: Re: Z or ZN and a couple other fx 260 to excel conversions


> Guy wrote
>
>> I was working out a problem here are the particluars
>> DR 40 deg 9 min N
>> 45 deg W
>> object Regulus
>> Dec 11deg 59. 9 min N
>> LHA 16:25:48
>> HC 58 Deg 20.4 Min
>> Using HO 249 the Z is 150 and the ZN is 210 I also checked with the star
>> section and the ZN was the same.
>> When I did the calculations using
>> Cos rasied to -1 (Zn) = sin (dec) - Sin (lat) x sin (Hc) / cos (Hc) x cos
>> (lat)
>>
>> The answer came out to 148 deg 11.4 min which is close to the 150 Z
>> however I
>> though that formula gave me the Zn?
>
> Yes and no, it is situational as the HC can be the same at some point
> before
> and some point after noon (using the sun as an example). With the sun LAN
> (local area noon, sun at its highest point) is also the upper meridian
> passage. For any body, LHA = 0 for upper meridian passage.  To extract Zn
> from Z,  determine whether the body is rising (pre meridian passage) or
> setting (post meridian passage.
>
> If rising, Zn = Z.  If setting, Zn = 360 - Z.
>
> When in doubt, if the sine of LHA is positive, Zn = 360 - Z.  When the
> sine
> of LHA is negative, Zn = Z.
>
> My memory device is "plus minus."  When the sign of sine LHA is PLUS, Zn =
> 360 MINUS Z.
>
> Bill
>
>
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