Merge pull request mourner#64 from Fabiz/master

fixed bug on calculation of astronomical refraction

suncalc.js

@@ -43,6 +43,14 @@ function altitude(H, phi, dec) { return asin(sin(phi) * sin(dec) + cos(phi) * co
 
 function siderealTime(d, lw) { return rad * (280.16 + 360.9856235 * d) - lw; }
 
+function astroRefraction(h) {
+    if (h < 0) // the following formula works for positive altitudes only.
+        h = 0; // if h = -0.08901179 a div/0 would occur.
+
+    // formula 16.4 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
+    // 1.02 / tan(h + 10.26 / (h + 5.10)) h in degrees, result in arc minutes -> converted to rad:
+    return 0.0002967 / Math.tan(h + 0.00312536 / (h + 0.08901179));
+}
 
 // general sun calculations
 
@@ -197,8 +205,7 @@ SunCalc.getMoonPosition = function (date, lat, lng) {
         // formula 14.1 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
         pa = atan(sin(H), tan(phi) * cos(c.dec) - sin(c.dec) * cos(H));
 
-    // altitude correction for refraction
-    h = h + rad * 0.017 / tan(h + rad * 10.26 / (h + rad * 5.10));
+    h = h + astroRefraction(h); // altitude correction for refraction
 
     return {
         azimuth: azimuth(H, phi, c.dec),

test.js

@@ -48,7 +48,7 @@ t.test('getMoonPosition returns moon position data given time and location', fun
     var moonPos = SunCalc.getMoonPosition(date, lat, lng);
 
     t.ok(near(moonPos.azimuth, -0.9783999522438226), 'azimuth');
-    t.ok(near(moonPos.altitude, 0.006969727754891917), 'altitude');
+    t.ok(near(moonPos.altitude, 0.014551482243892251), 'altitude');
     t.ok(near(moonPos.distance, 364121.37256256194), 'distance');
     t.end();
 });
@@ -65,8 +65,8 @@ t.test('getMoonIllumination returns fraction and angle of moon\'s illuminated li
 t.test('getMoonTimes returns moon rise and set times', function (t) {
     var moonTimes = SunCalc.getMoonTimes(new Date('2013-03-04UTC'), lat, lng, true);
 
-    t.equal(moonTimes.rise.toUTCString(), 'Mon, 04 Mar 2013 23:57:55 GMT');
-    t.equal(moonTimes.set.toUTCString(), 'Mon, 04 Mar 2013 07:28:41 GMT');
+    t.equal(moonTimes.rise.toUTCString(), 'Mon, 04 Mar 2013 23:54:29 GMT');
+    t.equal(moonTimes.set.toUTCString(), 'Mon, 04 Mar 2013 07:47:58 GMT');
 
     t.end();
 });