37 lines
1.0 KiB
Go
37 lines
1.0 KiB
Go
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package eclipse
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import (
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"math"
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"b612.me/astro/basic"
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)
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const (
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eclipseSeasonNodeDistanceLimitDeg = 35.0
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eclipseSeasonMaxSearchStep = 4
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)
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func nextEclipseSearchCandidateTT(candidateTT float64, phaseType, direction int, synodicMonthDays float64) float64 {
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step := eclipseSearchStep(candidateTT, direction, synodicMonthDays)
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return basic.CalcMoonSHByJDE(candidateTT+float64(direction*step)*synodicMonthDays, phaseType)
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}
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func eclipseSearchStep(candidateTT float64, direction int, synodicMonthDays float64) int {
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step := 1
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for nextStep := 2; nextStep <= eclipseSeasonMaxSearchStep; nextStep++ {
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skippedTT := candidateTT + float64(direction*(nextStep-1))*synodicMonthDays
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if eclipseNodeDistance(skippedTT) < eclipseSeasonNodeDistanceLimitDeg {
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break
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}
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step = nextStep
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}
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return step
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}
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func eclipseNodeDistance(ttJDE float64) float64 {
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argument := normalizeDegree360(basic.MoonLonX(ttJDE))
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toAscending := math.Min(argument, 360-argument)
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toDescending := math.Abs(argument - 180)
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return math.Min(toAscending, toDescending)
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}
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