Commit: 26bcf55822737f24df800d73055d3ad4865e114b
Parent: 0198e415862c729649fc7e7acca860406cdbc629
Author: Vi Grey
Date: 2023-10-26 01:00 UTC
Summary: More accurate disc angle calculation

 src/syzygy.go | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)


diff --git a/src/syzygy.go b/src/syzygy.go
index dfb6800..678f0f0 100644
--- a/src/syzygy.go
+++ b/src/syzygy.go
@@ -519,19 +519,25 @@ type xy struct {
 
 // Get atmostpheric refraction of object at alt
 func getAtmosphericRefraction(alt float64) float64 {
-	r := 1.02 / math.Tan((alt+(10.3/(alt+5.11)))/360*2*math.Pi)
+	r := 1.02 / math.Tan(degreesToRadians(alt+(10.3/(alt+5.11))))
 	return r * ((1013.25 / 1010) * (283 / 288.0)) / 60
 }
 
 // Get apparent altitude due to refraction of object in the sky
 // based on its distance, radius, and actual angle in the sky
 func getApparentAltitude(dist, radius, angle float64) float64 {
-	discAngle := math.Atan(radius/dist) / (2 * math.Pi) * 360
+	discAngle := getDiscAngle(dist, radius)
 	alt := angle - 90 + discAngle
 	refraction := getAtmosphericRefraction(alt)
 	return alt + refraction
 }
 
+// Get object disc angle in degrees for object dist distance away with
+// given radius.  Angle is in
+func getDiscAngle(dist, radius float64) float64 {
+	return radiansToDegrees(math.Asin(radius / dist))
+}
+
 // (47.1) Astronomical Algorithms, 2nd Edition p 338
 // Moon Mean Longitude
 // t is time measured in Julian centuries from the