40 lines
1.5 KiB
Go
40 lines
1.5 KiB
Go
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package basic
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import . "b612.me/astro/tools"
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// OrbitSunDistance 返回轨道目标在给定 TT/TDB 儒略日的日心距离，单位 AU。
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func OrbitSunDistance(jd float64, elements OrbitElements) float64 {
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_, _, distance := OrbitHeliocentricEclipticJ2000(jd, elements)
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return distance
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}
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// OrbitEarthDistance 返回轨道目标在给定 TT/TDB 儒略日的地心距离，单位 AU。
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func OrbitEarthDistance(jd float64, elements OrbitElements) float64 {
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_, _, distance := OrbitGeocentricEclipticJ2000(jd, elements)
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return distance
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}
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// OrbitPhaseAngle 返回轨道目标的相位角，单位度。
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func OrbitPhaseAngle(jd float64, elements OrbitElements) float64 {
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return ArcCos(orbitPhaseCosine(jd, elements))
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}
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// OrbitIlluminatedFraction 返回轨道目标的被照亮比例。
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func OrbitIlluminatedFraction(jd float64, elements OrbitElements) float64 {
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return (1 + orbitPhaseCosine(jd, elements)) / 2
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}
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// OrbitElongation 返回轨道目标相对于太阳的地心视角距，单位度。
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func OrbitElongation(jd float64, elements OrbitElements) float64 {
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lon, lat, _ := OrbitApparentGeocentricEcliptic(jd, elements)
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return StarAngularSeparation(lon, lat, HSunApparentLo(jd), HSunTrueBo(jd))
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}
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func orbitPhaseCosine(jd float64, elements OrbitElements) float64 {
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sunDistance := OrbitSunDistance(jd, elements)
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earthDistance := OrbitEarthDistance(jd, elements)
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earthSunDistance := EarthAway(jd)
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cosine := (sunDistance*sunDistance + earthDistance*earthDistance - earthSunDistance*earthSunDistance) / (2 * sunDistance * earthDistance)
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return clampUnit(cosine)
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}
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