68 lines
2.0 KiB
Go
68 lines
2.0 KiB
Go
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// Package formula 提供与具体时刻、星历表无关的研究型天文公式。
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package formula
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import "math"
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const (
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planckConstant = 6.62607015e-34
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speedOfLight = 299792458.0
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boltzmannConstant = 1.380649e-23
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stefanBoltzmannConstant = 5.670374419e-8
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wienDisplacementConstant = 2.897771955e-3
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)
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// WienPeakWavelength 维恩峰值波长 / Wien peak wavelength.
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//
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// temperatureK: 黑体温度，单位开尔文
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//
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// 返回：
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//
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// 峰值波长，单位米
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func WienPeakWavelength(temperatureK float64) float64 {
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if temperatureK <= 0 || math.IsNaN(temperatureK) || math.IsInf(temperatureK, 0) {
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return math.NaN()
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}
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return wienDisplacementConstant / temperatureK
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}
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// StefanBoltzmannFlux 斯特藩-玻尔兹曼通量 / Stefan-Boltzmann flux.
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//
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// temperatureK: 黑体温度，单位开尔文
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//
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// 返回：
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//
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// 单位面积总出射度，单位 W/m^2
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func StefanBoltzmannFlux(temperatureK float64) float64 {
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if temperatureK < 0 || math.IsNaN(temperatureK) || math.IsInf(temperatureK, 0) {
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return math.NaN()
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}
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return stefanBoltzmannConstant * math.Pow(temperatureK, 4)
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}
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// PlanckRadianceByWavelength 按波长的普朗克谱辐亮度 / Planck spectral radiance by wavelength.
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//
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// wavelengthM: 波长，单位米
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// temperatureK: 黑体温度，单位开尔文
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//
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// 返回：
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//
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// 谱辐亮度，单位 W·sr^-1·m^-3
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//
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// 例：
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//
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// b := formula.PlanckRadianceByWavelength(500e-9, 5772)
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func PlanckRadianceByWavelength(wavelengthM, temperatureK float64) float64 {
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if wavelengthM <= 0 || temperatureK <= 0 ||
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math.IsNaN(wavelengthM) || math.IsInf(wavelengthM, 0) ||
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math.IsNaN(temperatureK) || math.IsInf(temperatureK, 0) {
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return math.NaN()
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}
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exponent := planckConstant * speedOfLight / (wavelengthM * boltzmannConstant * temperatureK)
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denominator := math.Expm1(exponent)
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if denominator == 0 {
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return math.Inf(1)
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}
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return 2 * planckConstant * speedOfLight * speedOfLight / math.Pow(wavelengthM, 5) / denominator
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}
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