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2026-10-21 19:32:02 -04:00
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+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.sunPos = sunPos;
+var _constants = require("./constants");
+////////////////////////////////////////////////////////////////////////////////////
+/* Line by Line MATLAB-to-Javascript conversion of "sun.mat" from Vallado package */
+////////////////////////////////////////////////////////////////////////////////////
+/* -----------------------------------------------------------------------------
+ *
+ *                              function sunPos
+ *
+ *  this function calculates the geocentric equatorial position vector
+ *      the sun given the julian date.  this is the low precision formula and
+ *      is valid for years from 1950 to 2050.  accuaracy of apparent coordinates
+ *      is 0.01  degrees.  notice many of the calculations are performed in
+ *      degrees, and are not changed until later.  this is due to the fact that
+ *      the almanac uses degrees exclusively in their formulations.
+ *
+ *  author        : david vallado                  719-573-2600    1 mar 2001
+ *
+ *  inputs          description                       range / units
+ *      jd          - julian date                       days from 4713 bc
+ *
+ *  outputs       :
+ *      rsun        - ijk position vector of the sun    au
+ *      rtasc       - right ascension                   rad
+ *      decl        - declination                       rad
+ *
+ *  coupling      :
+ *      -
+ *
+ *  references    :
+ *      VALLADO, DAVID A. (2022) ‘Computer software in MATLAB’, in Fundamentals of astrodynamics and applications. 5th edn.
+ *      Computer software in MATLAB: http://celestrak.org/software/vallado-sw.php
+ *  --------------------------------------------------------------------------- */
+function sunPos(jday) {
+  // -------------------------  implementation   -----------------
+  // -------------------  initialize values   --------------------
+  var tut1 = (jday - 2451545) / 36525;
+  var meanlong = (280.460 + 36000.77 * tut1) % 360; //deg
+  var ttdb = tut1; // is this declaration required instead of replacing `ttdb` with `tut1`
+  var meananomaly = (357.5277233 + 35999.05034 * ttdb * _constants.deg2rad) % _constants.twoPi; //rad
+  if (meananomaly < 0) {
+    meananomaly += _constants.twoPi;
+  }
+  var eclplong_raw = (meanlong + 1.914666471 * Math.sin(meananomaly) + 0.019994643 * Math.sin(2.0 * meananomaly)) % 360.0 * _constants.deg2rad; //rad
+  var obliquity = (23.439291 - 0.0130042 * ttdb) * _constants.deg2rad; //rad
+  // --------- find magnitude of sun vector, and it's components ------
+  var magr = 1.000140612 - 0.016708617 * Math.cos(meananomaly) - 0.000139589 * Math.cos(2.0 * meananomaly); // in au's
+  var rsun = [magr * Math.cos(eclplong_raw), magr * Math.cos(obliquity) * Math.sin(eclplong_raw), magr * Math.sin(obliquity) * Math.sin(eclplong_raw)];
+  var rtasc_raw = Math.atan(Math.cos(obliquity) * Math.tan(eclplong_raw));
+  // --- check that rtasc is in the same quadrant as eclplong_raw ----
+  var eclplong = eclplong_raw;
+  if (eclplong < 0.0) {
+    eclplong += _constants.twoPi; // make sure it's in 0 to 2pi range
+  }
+  var rtasc = rtasc_raw;
+  if (Math.abs(eclplong_raw - rtasc) > _constants.pi * 0.5) {
+    rtasc += 0.5 * _constants.pi * Math.round((eclplong_raw - rtasc_raw) / (0.5 * _constants.pi));
+  }
+  var decl = Math.asin(Math.sin(obliquity) * Math.sin(eclplong_raw));
+  return {
+    rsun: rsun,
+    rtasc: rtasc,
+    decl: decl
+  };
+}
+/* Original MATLAB code for Sun position from Vallado package (sun.mat)  */
+/*
+function [rsun,rtasc,decl] = sun ( jd );
+
+        twopi      =     2.0*pi;
+        deg2rad    =     pi/180.0;
+        show = 'n';
+
+        % -------------------------  implementation   -----------------
+        % -------------------  initialize values   --------------------
+        tut1= ( jd - 2451545.0  )/ 36525.0;
+
+        if show == 'y'
+            fprintf(1,'tut1 %14.9f \n',tut1);
+        end
+
+        meanlong= 280.460  + 36000.77*tut1;
+        meanlong= rem( meanlong,360.0  );  %deg
+
+        ttdb= tut1;
+        meananomaly= 357.5277233  + 35999.05034 *ttdb;
+        meananomaly= rem( meananomaly*deg2rad,twopi );  %rad
+        if ( meananomaly < 0.0  )
+            meananomaly= twopi + meananomaly;
+        end
+
+        eclplong_raw= meanlong + 1.914666471 *sin(meananomaly) ...
+                    + 0.019994643 *sin(2.0 *meananomaly); %deg
+        eclplong_raw= rem( eclplong_raw,360.0  );  %deg
+
+        obliquity= 23.439291  - 0.0130042 *ttdb;  %deg
+
+        eclplong_raw = eclplong_raw *deg2rad;
+        obliquity= obliquity *deg2rad;
+
+        % --------- find magnitude of sun vector, )   components ------
+        magr= 1.000140612  - 0.016708617 *cos( meananomaly ) ...
+                              - 0.000139589 *cos( 2.0 *meananomaly );    % in au's
+
+        rsun(1)= magr*cos( eclplong_raw );
+        rsun(2)= magr*cos(obliquity)*sin(eclplong_raw);
+        rsun(3)= magr*sin(obliquity)*sin(eclplong_raw);
+
+        if show == 'y'
+            fprintf(1,'meanlon %11.6f meanan %11.6f eclplon %11.6f obli %11.6f \n', ...
+                    meanlong,meananomaly/deg2rad,eclplong_raw/deg2rad,obliquity/deg2rad);
+            fprintf(1,'rs %11.9f %11.9f %11.9f \n',rsun);
+            fprintf(1,'magr %14.7f \n',magr);
+        end
+
+        rtasc= atan( cos(obliquity)*tan(eclplong_raw) );
+
+        % --- check that rtasc is in the same quadrant as eclplong_raw ----
+        if ( eclplong_raw < 0.0  )
+            eclplong_raw= eclplong_raw + twopi;    % make sure it's in 0 to 2pi range
+        end
+        if ( abs( eclplong_raw-rtasc ) > pi*0.5  )
+            rtasc= rtasc + 0.5 *pi*round( (eclplong_raw-rtasc)/(0.5 *pi));
+        end
+        decl = asin( sin(obliquity)*sin(eclplong_raw) );
+*/