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Oblique Ascendant

 
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stcisz



Joined: 19 Nov 2016
Posts: 19

Posted: Mon Nov 21, 2016 6:22 pm    Post subject: Oblique Ascendant Reply with quote

I'm writing an astrological application based on "Radix System" by V.E. Robson. One of the thing to be computed is oblique ascendant i.e. the ascendant position when M.C, and location is given. I wrote following procedure:
Code:
function computeAsc(mc) {
   var T = (hor.jdate -  2451545.0) / 36525;
   var eta = 23 + 26/60 + 21.45/(60*60) -
      46.815/60 * T - 0.0006/60 * T * T + 0.00181/60 * T * T * T;
   var RAMC = Math.atan(Math.tan(mc * Math.PI / 180) *
         Math.cos(eta * Math.PI/180));
   y = -(Math.sin( RAMC) + Math.tan(eta * Math.PI / 180) *
         Math.tan(hor.latitude * Math.PI / 180)) *
         Math.cos(eta * Math.PI / 180)
   x = Math.cos(RAMC);
   asc = Math.atan2(x,y);
   return asc * 180 /Math.PI;
}
and got strange results. Could anyone point me where is an error.

Best regards,
Staszek
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skyrack



Joined: 02 Aug 2012
Posts: 168
Location: Thailand

Posted: Tue Nov 22, 2016 8:53 am    Post subject: Reply with quote

Is that javascript or?
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stcisz



Joined: 19 Nov 2016
Posts: 19

Posted: Tue Nov 22, 2016 9:01 am    Post subject: Reply with quote

Yes, it is.
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Ursa Major



Joined: 28 Jul 2010
Posts: 24
Location: Limburg

Posted: Tue Nov 22, 2016 9:07 am    Post subject: Reply with quote

I have changed your function in the following. Hope it helps.


var T = ( hor.jdate - 2451545.0 ) / 36525;
var eta = ( 84391.45 - 46.815 * T - 0.0006 * T * T + 0.00181 * T * T * T ) / 3600.0;
var RAMC = Math.atan( Math.tan( mc * Math.PI / 180 ) * Math.cos( eta * Math.PI / 180 ));

var OB = eta * Math.PI / 180;

y = -Math.sin( RAMC ) * Math.cos( OB ) - Math.tan( hor.latitude * Math.PI / 180 ) * Math.sin( OB );
x = Math.cos( RAMC );

asc = Math.atan2( x, y );

return asc * 180 / Math.PI;
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stcisz



Joined: 19 Nov 2016
Posts: 19

Posted: Tue Nov 22, 2016 6:36 pm    Post subject: Reply with quote

Thank you for interest. Unfortunately after change procedure the problem persist. For value of latitude 49.60889, jdate 2440704.6493055555 and mc 214.29666062554156 procedure returns 138.385708051255. This is close to directional Desc or about 180 degrees from an expected position.

Best regards,
Staszek
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Ursa Major



Joined: 28 Jul 2010
Posts: 24
Location: Limburg

Posted: Tue Nov 22, 2016 7:37 pm    Post subject: Reply with quote

You have to add lines between Var RAMC en Var OB
See the mail I send to you.

In short:

if RAMC less then 0 you have to add Math.PI to RAMC
if mc greater then Math.PI you have again add Math.PI to RAMC
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Ursa Major



Joined: 28 Jul 2010
Posts: 24
Location: Limburg

Posted: Wed Nov 23, 2016 1:36 pm    Post subject: Reply with quote

# Input given by you
mc = 214.29666062554156
hor.latitude = 49.60889
hor.jdate = 2440704.64931

I change your function in the following:
------------------------------------------------------------
Var T = ( hor.jdate - 2451545.0 ) / 36525;
Var eta = ( 84391.45 - 46.815 * T - 0.0006 * T * T + 0.00181 * T * T * T ) / 3600.0;
Var ob = Math.radians( eta );

y = - Math.sin( Math.radians( mc )) * Math.cos( ob ) - Math.tan( Math.radians( hor.latitude )) * Math.sin( ob ) ;
x = Math.cos( Math.radians( mc ));

asc = Math.atan2( x, y ) ;
asc = Math.degrees( asc ) ;

if asc < 0 : asc = asc + 360;

return asc;

--------------------------------------------

It gives as result: 273.414872 ...

With best regards,
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stcisz



Joined: 19 Nov 2016
Posts: 19

Posted: Wed Nov 23, 2016 2:57 pm    Post subject: Reply with quote

Looks that those formulas works. Thank you very much.

Best regards,
Staszek
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