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Fix longitude sign bug #5

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Fix longitude sign bug #5

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12 changes: 8 additions & 4 deletions astrotime.go
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Original file line number Diff line number Diff line change
@@ -1,11 +1,11 @@
// NAA - NOAA's Astronomical Algorithms
package astrotime

// (JavaScript web page
// (JavaScript web page
// http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html by
// Chris Cornwall, Aaron Horiuchi and Chris Lehman)
// Ported to C++ by Pete Gray ([email protected]), July 2006
// Released as Open Source and can be used in any way, as long as the
// Released as Open Source and can be used in any way, as long as the
// above description remains in place.

import (
Expand Down Expand Up @@ -306,10 +306,12 @@ func calcSunriseUTC(jd float64, latitude float64, longitude float64) float64 {
return timeUTC
}

// CalcSunrise calculates the sunrise, in local time, on the day t at the
// CalcSunrise calculates the sunrise, in local time, on the day t at the
// location specified in longitude and latitude.
// For why we flip the sign on longitude, see: http://www.esrl.noaa.gov/gmd/grad/solcalc/sunrise.html
func CalcSunrise(t time.Time, latitude float64, longitude float64) time.Time {
jd := CalcJD(t)
longitude = -longitude
sunriseUTC := time.Duration(math.Floor(calcSunriseUTC(jd, latitude, longitude)*60) * 1e9)
loc, _ := time.LoadLocation("UTC")
return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc).Add(sunriseUTC).In(t.Location())
Expand Down Expand Up @@ -377,10 +379,12 @@ func calcSunsetUTC(jd float64, latitude float64, longitude float64) float64 {
return 720 + timeDiff - eqTime
}

// CalcSunset calculates the sunset, in local time, on the day t at the
// CalcSunset calculates the sunset, in local time, on the day t at the
// location specified in longitude and latitude.
// For why we flip the sign on longitude, see: http://www.esrl.noaa.gov/gmd/grad/solcalc/sunrise.html
func CalcSunset(t time.Time, latitude float64, longitude float64) time.Time {
jd := CalcJD(t)
longitude = -longitude
sunsetUTC := time.Duration(math.Floor(calcSunsetUTC(jd, latitude, longitude)*60) * 1e9)
loc, _ := time.LoadLocation("UTC")
return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, loc).Add(sunsetUTC).In(t.Location())
Expand Down