Merge pull request #23 from jfcarr-astronomy/sun/solar-elongation

Calculate -> Solar elongation

PALib.Tests/PASun.cs

@@ -47,5 +47,11 @@ public void EquationOfTime()
 		{
 			Assert.Equal((6, 31.52), _paSun.EquationOfTime(27, 7, 2010));
 		}
+
+		[Fact]
+		public void SolarElongation()
+		{
+			Assert.Equal(24.78, _paSun.SolarElongation(10, 6, 45, 11, 57, 27, 27.8333333, 7, 2010));
+		}
 	}
 }

PALib/PAMacros.cs

@@ -2607,5 +2607,41 @@ public static (double a, double x, double y, double la, string s) ETwilight_L371
 
 			return (a, x, y, la, s);
 		}
+
+		/// <summary>
+		/// Calculate the angle between two celestial objects
+		/// </summary>
+		/// <remarks>
+		/// Original macro name: Angle
+		/// </remarks>
+		/// <param name="xx1"></param>
+		/// <param name="xm1"></param>
+		/// <param name="xs1"></param>
+		/// <param name="dd1"></param>
+		/// <param name="dm1"></param>
+		/// <param name="ds1"></param>
+		/// <param name="xx2"></param>
+		/// <param name="xm2"></param>
+		/// <param name="xs2"></param>
+		/// <param name="dd2"></param>
+		/// <param name="dm2"></param>
+		/// <param name="ds2"></param>
+		/// <param name="s"></param>
+		/// <returns></returns>
+		public static double Angle(double xx1, double xm1, double xs1, double dd1, double dm1, double ds1, double xx2, double xm2, double xs2, double dd2, double dm2, double ds2, PAAngleMeasure s
+		)
+		{
+			var a = (s.Equals(PAAngleMeasure.Hours)) ? DegreeHoursToDecimalDegrees(HMStoDH(xx1, xm1, xs1)) : DegreesMinutesSecondsToDecimalDegrees(xx1, xm1, xs1);
+			var b = a.ToRadians();
+			var c = DegreesMinutesSecondsToDecimalDegrees(dd1, dm1, ds1);
+			var d = c.ToRadians();
+			var e = (s.Equals(PAAngleMeasure.Hours)) ? DegreeHoursToDecimalDegrees(HMStoDH(xx2, xm2, xs2)) : DegreesMinutesSecondsToDecimalDegrees(xx2, xm2, xs2);
+			var f = e.ToRadians();
+			var g = DegreesMinutesSecondsToDecimalDegrees(dd2, dm2, ds2);
+			var h = g.ToRadians();
+			var i = (d.Sine() * h.Sine() + d.Cosine() * h.Cosine() * (b - f).Cosine()).ACosine();
+
+			return Degrees(i);
+		}
 	}
 }

PALib/PASun.cs

@@ -240,5 +240,31 @@ public class PASun
 
 			return (equationOfTimeMin, equationOfTimeSec);
 		}
+
+		/// <summary>
+		/// Calculate solar elongation for a celestial body.
+		/// </summary>
+		/// <remarks>
+		/// Solar elongation is the angle between the lines of sight from the Earth to the Sun and from the Earth to the celestial body.
+		/// </remarks>
+		/// <param name="raHour"></param>
+		/// <param name="raMin"></param>
+		/// <param name="raSec"></param>
+		/// <param name="decDeg"></param>
+		/// <param name="decMin"></param>
+		/// <param name="decSec"></param>
+		/// <param name="gwdateDay"></param>
+		/// <param name="gwdateMonth"></param>
+		/// <param name="gwdateYear"></param>
+		/// <returns>solarElongationDeg -- Solar elongation, in degrees</returns>
+		public double SolarElongation(double raHour, double raMin, double raSec, double decDeg, double decMin, double decSec, double gwdateDay, int gwdateMonth, int gwdateYear)
+		{
+			var sunLongitudeDeg = PAMacros.SunLong(0, 0, 0, 0, 0, gwdateDay, gwdateMonth, gwdateYear);
+			var sunRAHours = PAMacros.DecimalDegreesToDegreeHours(PAMacros.EcRA(sunLongitudeDeg, 0, 0, 0, 0, 0, gwdateDay, gwdateMonth, gwdateYear));
+			var sunDecDeg = PAMacros.EcDec(sunLongitudeDeg, 0, 0, 0, 0, 0, gwdateDay, gwdateMonth, gwdateYear);
+			var solarElongationDeg = PAMacros.Angle(sunRAHours, 0, 0, sunDecDeg, 0, 0, raHour, raMin, raSec, decDeg, decMin, decSec, PAAngleMeasure.Hours);
+
+			return Math.Round(solarElongationDeg, 2);
+		}
 	}
 }

PALib/PATypes.cs

@@ -13,4 +13,10 @@ public enum PATwilightType
 		Nautical = 12,
 		Astronomical = 18
 	}
+
+	public enum PAAngleMeasure
+	{
+		Degrees,
+		Hours
+	}
 }

README.md

@@ -44,7 +44,7 @@ If you're interested in this topic, please buy the book! It provides far more de
 - [x] Calculate -> Local sunrise and sunset
 - [x] Calculate -> Morning and evening twilight
 - [x] Calculate -> Equation of time
-- [ ] Calculate -> Solar elongation
+- [x] Calculate -> Solar elongation
 
 ### Planets