C# Sunrise/Sunset with latitude/longitude

Question

Is there a way in C# to calculate given a latitude and longitude when the sun will set and rise for a given day?

Answer 1

CoordinateSharp is available as a Nuget package. It's a standalone package that can handle sun and moon times.

//UTC Date 21-MAR-2019 @ 11:00 AM
DateTime d = new DateTime(2017,3,21,11,0,0);
Coordinate c = new Coordinate(40.57682, -70.75678, d);
c.CelestialInfo.SunRise.ToString(); //Outputs 3/21/2017 10:45:00 AM

It can handle local time, and gives a lot of additional info such as dawn/dusk, eclipse, coordinate data, and more. More info on how to use here:

https://coordinatesharp.com/DeveloperGuide#accessing-celestial-data

Answer 2

I have tested this nuget package in UWP.

https://www.nuget.org/packages/SolarCalculator/

The documentation is a bit sketchy, and is here:

https://github.com/porrey/Solar-Calculator

You can use this to get the sunrise, given

la = latitude; and lo = longitude; for your area:

            SolarTimes solarTimes = new SolarTimes(DateTime.Now, la, lo);
            DateTime sr = solarTimes.Sunrise;
            DateTime dt = Convert.ToDateTime(sr);
            textblockb.Text = dt.ToString("h:mm:ss");

You can install it in Visual Studio using the PM manager

Install-Package SolarCalculator -Version 2.0.2 

or by looking up SolarCalculator in the "Manage NuGet Packages" Visual Studio library.

Answer 3

Yes quit a few.

A few links for patterns.

http://williams.best.vwh.net/sunrise_sunset_example.htm

http://www.codeproject.com/Articles/29306/C-Class-for-Calculating-Sunrise-and-Sunset-Times

https://social.msdn.microsoft.com/Forums/vstudio/en-US/a4fad4c3-6d18-41fc-82b7-1f3031349837/get-sunrise-and-sunset-time-based-on-latitude-and-longitude?forum=csharpgeneral

https://gist.github.com/cstrahan/767532

http://pointofint.blogspot.com/2014/06/sunrise-and-sunset-in-c.html

http://yaddb.blogspot.com/2013/01/how-to-calculate-sunrise-and-sunset.html

https://forums.asp.net/t/1810934.aspx?Sunrise+and+Sunset+timings+Calculation+

http://www.ip2location.com/tutorials/display-sunrise-sunset-time-using-csharp-and-mysql-database

http://en.pudn.com/downloads270/sourcecode/windows/csharp/detail1235934_en.html

http://regator.com/p/25716249/c_class_for_calculating_sunrise_and_sunset_times

http://forums.xkcd.com/viewtopic.php?t=102253

http://www.redrok.com/solar_position_algorithm.pdf

http://sidstation.loudet.org/sunazimuth-en.xhtml

https://sourceforge.net/directory/os:windows/?q=sunrise/set%20times

https://www.nuget.org/packages/SolarCalculator/

http://www.grasshopper3d.com/forum/topics/solar-calculation-plugin

and this was a project that I did for Planet Source Code long ago but luckily I saved it elsewhere because that site lost data.

https://github.com/DouglasAllen/SunTimes.VSCS.Net

uses this Gist plus

https://gist.github.com/DouglasAllen/c682e4c412a0b9d8f536b014c1766f20

Now for a brief explanation of the technique to do that.

First for any day you need true solar noon or transit for your location.

That takes into account your local longitude. It may be converted to a time just by dividing it by 15.

That is how much time later you are from Zulu zone time or zero longitude.

That starts at 12:00 PM or Noon.

And on your time calculated from the longitude.

Now the hard part. You need a way to calculate the Equation of Time.

That is a time difference caused by Earth tilt and orbit around the Sun.

This will give you an idea... https://en.wikipedia.org/wiki/Equation_of_time

But they have a formula that is much easier.... https://en.wikipedia.org/wiki/Sunrise_equation

This guy has some books that a lot of people go by or buy. :-D https://en.wikipedia.org/wiki/Jean_Meeus

Use your first calculation for your mean solar transit and calculate a JDN... https://en.wikipedia.org/wiki/Julian_day

This gets used by all the angle formulas as a time in Julian century https://en.wikipedia.org/wiki/Julian_year_(astronomy)

https://en.wikipedia.org/wiki/Epoch_(astronomy)

It's basically your JDN minus the epoch such as J2000 or 2451545.0 all divided by 36525.0 to give you the Julian century or t which gets used for most formula that have t as a parameter. Sometimes Julian millennia is used. In that case it's 3652500.0

The trick is to find those angle formulas that help you solve the Equation of Time.

Then you get your true solar transit and subtract the half day or add the half day of sunlight for your location. You'll find those around in the answers and the software.

Once you get something going you can check it against a search for the times or online calculators.

I hope this is enough to get you going. There are libraries all over the place but it's not that hard to make your own. I did but it's in Ruby. It could prove useful....https://github.com/DouglasAllen/gem-equationoftime

good luck!

Answer 4

VB.Net version of dotsa's answer, which can also determine time-zones automatically.

Output (checked by watching the sunset this evening):

Main.VB:

Module Main

Sub Main()

    ' http://www.timeanddate.com/sun/usa/seattle
    ' http://www.esrl.noaa.gov/gmd/grad/solcalc/

    ' Vessy, Switzerland
    Dim latitude As Double = 46.17062
    Dim longitude As Double = 6.161667
    Dim dst As Boolean = True
    Dim timehere As DateTime = DateTime.Now

    Console.WriteLine("It is currently {0:HH:mm:ss} UTC", DateTime.UtcNow)
    Console.WriteLine("The time here, at {0}°,{1}° is {2:HH:mm:ss}", latitude, longitude, timehere)
    Dim local As TimeZoneInfo = TimeZoneInfo.Local
    Dim zone As Integer = local.BaseUtcOffset().TotalHours

    If local.SupportsDaylightSavingTime Then
        Dim standard As String = local.StandardName
        Dim daylight As String = local.DaylightName
        dst = local.IsDaylightSavingTime(timehere)
        Dim current As String = IIf(dst, daylight, standard)
        Console.WriteLine("Daylight-saving time is supported here. Current offset {0:+0} hours, {1}", zone, current)
    Else
        Console.WriteLine("Daylight-saving time is not supported here")
    End If

    System.Console.WriteLine("Sunrise today {0}", Sunrises(latitude, longitude))
    System.Console.WriteLine("Sunset  today {0}", Sunsets(latitude, longitude))
    System.Console.ReadLine()
End Sub

End Module

Sun.vb:

Public Module Sun
' Get sunrise time at latitude, longitude using local system timezone
Function Sunrises(latitude As Double, longitude As Double) As DateTime
    Dim julian As Double = JulianDay(DateTime.Now)
    Dim rises As Double = SunRiseUTC(julian, latitude, longitude)
    Dim timehere As DateTime = DateTime.Now
    Dim local As TimeZoneInfo = TimeZoneInfo.Local
    Dim dst As Boolean = local.IsDaylightSavingTime(timehere)
    Dim zone As Integer = local.BaseUtcOffset().TotalHours
    Dim result As DateTime = getDateTime(rises, zone, timehere, dst)
    Return result
End Function
' Get sunset time at latitude, longitude using local system timezone
Function Sunsets(latitude As Double, longitude As Double) As DateTime
    Dim julian As Double = JulianDay(DateTime.Now)
    Dim rises As Double = SunSetUTC(julian, latitude, longitude)
    Dim timehere As DateTime = DateTime.Now
    Dim local As TimeZoneInfo = TimeZoneInfo.Local
    Dim dst As Boolean = local.IsDaylightSavingTime(timehere)
    Dim zone As Integer = local.BaseUtcOffset().TotalHours
    Dim result As DateTime = getDateTime(rises, zone, timehere, dst)
    Return result
End Function
' Convert radian angle to degrees
Public Function Degrees(angleRad As Double) As Double
    Return (180.0 * angleRad / Math.PI)
End Function
' Convert degree angle to radians
Public Function Radians(angleDeg As Double) As Double
    Return (Math.PI * angleDeg / 180.0)
End Function
'* Name: JulianDay  
'* Type: Function   
'* Purpose: Julian day from calendar day    
'* Arguments:   
'* year : 4 digit year  
'* month: January = 1   
'* day : 1 - 31 
'* Return value:    
'* The Julian day corresponding to the date 
'* Note:    
'* Number is returned for start of day. Fractional days should be   
'* added later. 
Public Function JulianDay(year As Integer, month As Integer, day As Integer) As Double
    If month <= 2 Then
        year -= 1
        month += 12
    End If
    Dim A As Double = Math.Floor(year / 100.0)
    Dim B As Double = 2 - A + Math.Floor(A / 4)

    Dim julian As Double = Math.Floor(365.25 * (year + 4716)) + Math.Floor(30.6001 * (month + 1)) + day + B - 1524.5
    Return julian
End Function

Public Function JulianDay([date] As DateTime) As Double
    Return JulianDay([date].Year, [date].Month, [date].Day)
End Function

'***********************************************************************/
'* Name: JulianCenturies    
'* Type: Function   
'* Purpose: convert Julian Day to centuries since J2000.0.  
'* Arguments:   
'* julian : the Julian Day to convert   
'* Return value:    
'* the T value corresponding to the Julian Day  
'***********************************************************************/

Public Function JulianCenturies(julian As Double) As Double
    Dim T As Double = (julian - 2451545.0) / 36525.0
    Return T
End Function


'***********************************************************************/
'* Name: JulianDayFromJulianCentury 
'* Type: Function   
'* Purpose: convert centuries since J2000.0 to Julian Day.  
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* the Julian Day corresponding to the t value  
'***********************************************************************/

Public Function JulianDayFromJulianCentury(t As Double) As Double
    Dim julian As Double = t * 36525.0 + 2451545.0
    Return julian
End Function


'***********************************************************************/
'* Name: calGeomMeanLongSun 
'* Type: Function   
'* Purpose: calculate the Geometric Mean Longitude of the Sun   
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* the Geometric Mean Longitude of the Sun in degrees   
'***********************************************************************/

Public Function GemoetricMeanLongitude(t As Double) As Double
    Dim L0 As Double = 280.46646 + t * (36000.76983 + 0.0003032 * t)
    While L0 > 360.0
        L0 -= 360.0
    End While
    While L0 < 0.0
        L0 += 360.0
    End While
    Return L0
    ' in degrees
End Function


'***********************************************************************/
'* Name: calGeomAnomalySun  
'* Type: Function   
'* Purpose: calculate the Geometric Mean Anomaly of the Sun 
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* the Geometric Mean Anomaly of the Sun in degrees 
'***********************************************************************/

Public Function GemoetricMeanAnomaly(t As Double) As Double
    Dim M As Double = 357.52911 + t * (35999.05029 - 0.0001537 * t)
    Return M
    ' in degrees
End Function

'***********************************************************************/
'* Name: EarthOrbitEccentricity 
'* Type: Function   
'* Purpose: calculate the eccentricity of earth's orbit 
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* the unitless eccentricity    
'***********************************************************************/


Public Function EarthOrbitEccentricity(t As Double) As Double
    Dim e As Double = 0.016708634 - t * (0.000042037 + 0.0000001267 * t)
    Return e
    ' unitless
End Function

'***********************************************************************/
'* Name: SunCentre  
'* Type: Function   
'* Purpose: calculate the equation of center for the sun    
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* in degrees   
'***********************************************************************/


Public Function SunCentre(t As Double) As Double
    Dim m As Double = GemoetricMeanAnomaly(t)

    Dim mrad As Double = Radians(m)
    Dim sinm As Double = Math.Sin(mrad)
    Dim sin2m As Double = Math.Sin(mrad + mrad)
    Dim sin3m As Double = Math.Sin(mrad + mrad + mrad)

    Dim C As Double = sinm * (1.914602 - t * (0.004817 + 0.000014 * t)) + sin2m * (0.019993 - 0.000101 * t) + sin3m * 0.000289
    Return C
    ' in degrees
End Function

'***********************************************************************/
'* Name: SunTrueLongitude   
'* Type: Function   
'* Purpose: calculate the true longitude of the sun 
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* sun's true longitude in degrees  
'***********************************************************************/


Public Function SunTrueLongitude(t As Double) As Double
    Dim l0 As Double = GemoetricMeanLongitude(t)
    Dim c As Double = SunCentre(t)

    Dim O As Double = l0 + c
    Return O
    ' in degrees
End Function

'***********************************************************************/
'* Name: SunTrueAnomaly 
'* Type: Function   
'* Purpose: calculate the true anamoly of the sun   
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* sun's true anamoly in degrees    
'***********************************************************************/

Public Function SunTrueAnomaly(t As Double) As Double
    Dim m As Double = GemoetricMeanAnomaly(t)
    Dim c As Double = SunCentre(t)

    Dim v As Double = m + c
    Return v
    ' in degrees
End Function

'***********************************************************************/
'* Name: SunDistanceAU  
'* Type: Function   
'* Purpose: calculate the distance to the sun in AU 
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* sun radius vector in AUs 
'***********************************************************************/

Public Function SunDistanceAU(t As Double) As Double
    Dim v As Double = SunTrueAnomaly(t)
    Dim e As Double = EarthOrbitEccentricity(t)

    Dim R As Double = (1.000001018 * (1 - e * e)) / (1 + e * Math.Cos(Radians(v)))
    Return R
    ' in AUs
End Function

'***********************************************************************/
'* Name: SunApparentLongitude   
'* Type: Function   
'* Purpose: calculate the apparent longitude of the sun 
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* sun's apparent longitude in degrees  
'***********************************************************************/

Public Function SunApparentLongitude(t As Double) As Double
    Dim o As Double = SunTrueLongitude(t)

    Dim omega As Double = 125.04 - 1934.136 * t
    Dim lambda As Double = o - 0.00569 - 0.00478 * Math.Sin(Radians(omega))
    Return lambda
    ' in degrees
End Function

'***********************************************************************/
'* Name: MeanObliquityOfEcliptic    
'* Type: Function   
'* Purpose: calculate the mean obliquity of the ecliptic    
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* mean obliquity in degrees    
'***********************************************************************/

Public Function MeanObliquityOfEcliptic(t As Double) As Double
    Dim seconds As Double = 21.448 - t * (46.815 + t * (0.00059 - t * (0.001813)))
    Dim e0 As Double = 23.0 + (26.0 + (seconds / 60.0)) / 60.0
    Return e0
    ' in degrees
End Function

'***********************************************************************/
'* Name: calcObliquityCorrection    
'* Type: Function   
'* Purpose: calculate the corrected obliquity of the ecliptic   
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* corrected obliquity in degrees   
'***********************************************************************/

Public Function calcObliquityCorrection(t As Double) As Double
    Dim e0 As Double = MeanObliquityOfEcliptic(t)

    Dim omega As Double = 125.04 - 1934.136 * t
    Dim e As Double = e0 + 0.00256 * Math.Cos(Radians(omega))
    Return e
    ' in degrees
End Function

'***********************************************************************/
'* Name: SunRightAscension  
'* Type: Function   
'* Purpose: calculate the right ascension of the sun    
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* sun's right ascension in degrees 
'***********************************************************************/

Public Function SunRightAscension(t As Double) As Double
    Dim e As Double = calcObliquityCorrection(t)
    Dim lambda As Double = SunApparentLongitude(t)

    Dim tananum As Double = (Math.Cos(Radians(e)) * Math.Sin(Radians(lambda)))
    Dim tanadenom As Double = (Math.Cos(Radians(lambda)))
    Dim alpha As Double = Degrees(Math.Atan2(tananum, tanadenom))
    Return alpha
    ' in degrees
End Function

'***********************************************************************/
'* Name: SunDeclination 
'* Type: Function   
'* Purpose: calculate the declination of the sun    
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* sun's declination in degrees 
'***********************************************************************/

Public Function SunDeclination(t As Double) As Double
    Dim e As Double = calcObliquityCorrection(t)
    Dim lambda As Double = SunApparentLongitude(t)

    Dim sint As Double = Math.Sin(Radians(e)) * Math.Sin(Radians(lambda))
    Dim theta As Double = Degrees(Math.Asin(sint))
    Return theta
    ' in degrees
End Function

'***********************************************************************/
'* Name: TrueSolarToMeanSolar   
'* Type: Function   
'* Purpose: calculate the difference between true solar time and mean   
'*   solar time 
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* Return value:    
'* equation of time in minutes of time  
'***********************************************************************/

Public Function TrueSolarToMeanSolar(t As Double) As Double
    Dim epsilon As Double = calcObliquityCorrection(t)
    Dim l0 As Double = GemoetricMeanLongitude(t)
    Dim e As Double = EarthOrbitEccentricity(t)
    Dim m As Double = GemoetricMeanAnomaly(t)

    Dim y As Double = Math.Tan(Radians(epsilon) / 2.0)
    y *= y

    Dim sin2l0 As Double = Math.Sin(2.0 * Radians(l0))
    Dim sinm As Double = Math.Sin(Radians(m))
    Dim cos2l0 As Double = Math.Cos(2.0 * Radians(l0))
    Dim sin4l0 As Double = Math.Sin(4.0 * Radians(l0))
    Dim sin2m As Double = Math.Sin(2.0 * Radians(m))

    Dim Etime As Double = y * sin2l0 - 2.0 * e * sinm + 4.0 * e * y * sinm * cos2l0 - 0.5 * y * y * sin4l0 - 1.25 * e * e * sin2m

    Return Degrees(Etime) * 4.0
    ' in minutes of time
End Function

'***********************************************************************/
'* Name: SunriseHourAngle   
'* Type: Function   
'* Purpose: calculate the hour angle of the sun at sunrise for the  
'*   latitude   
'* Arguments:   
'* lat : latitude of observer in degrees    
'*  solarDec : declination angle of sun in degrees  
'* Return value:    
'* hour angle of sunrise in radians 
'***********************************************************************/

Public Function SunriseHourAngle(lat As Double, solarDec As Double) As Double
    Dim latRad As Double = Radians(lat)
    Dim sdRad As Double = Radians(solarDec)

    Dim HAarg As Double = (Math.Cos(Radians(90.833)) / (Math.Cos(latRad) * Math.Cos(sdRad)) - Math.Tan(latRad) * Math.Tan(sdRad))

    Dim HA As Double = (Math.Acos(Math.Cos(Radians(90.833)) / (Math.Cos(latRad) * Math.Cos(sdRad)) - Math.Tan(latRad) * Math.Tan(sdRad)))

    Return HA
    ' in radians
End Function

'***********************************************************************/
'* Name: SunsetHourAngle    
'* Type: Function   
'* Purpose: calculate the hour angle of the sun at sunset for the   
'*   latitude   
'* Arguments:   
'* lat : latitude of observer in degrees    
'*  solarDec : declination angle of sun in degrees  
'* Return value:    
'* hour angle of sunset in radians  
'***********************************************************************/

Public Function SunsetHourAngle(lat As Double, solarDec As Double) As Double
    Dim latRad As Double = Radians(lat)
    Dim sdRad As Double = Radians(solarDec)

    Dim HAarg As Double = (Math.Cos(Radians(90.833)) / (Math.Cos(latRad) * Math.Cos(sdRad)) - Math.Tan(latRad) * Math.Tan(sdRad))

    Dim HA As Double = (Math.Acos(Math.Cos(Radians(90.833)) / (Math.Cos(latRad) * Math.Cos(sdRad)) - Math.Tan(latRad) * Math.Tan(sdRad)))

    Return -HA
    ' in radians
End Function


'***********************************************************************/
'* Name: SunRiseUTC 
'* Type: Function   
'* Purpose: calculate the Universal Coordinated Time (UTC) of sunrise   
'*   for the given day at the given location on earth   
'* Arguments:   
'* julian : julian day  
'* latitude : latitude of observer in degrees   
'* longitude : longitude of observer in degrees 
'* Return value:    
'* time in minutes from zero Z  
'***********************************************************************/

'Public  Function SunRiseUTC(julian As Double, latitude As Double, longitude As Double) As Double
'    Dim t As Double = JulianCenturies(julian)

'    ' *** Find the time of solar noon at the location, and use
'    ' that declination. This is better than start of the 
'    ' Julian day

'    Dim noonmin As Double = SolarNoonUTC(t, longitude)
'    Dim tnoon As Double = JulianCenturies(julian + noonmin / 1440.0)

'    ' *** First pass to approximate sunrise (using solar noon)

'    Dim eqTime As Double = TrueSolarToMeanSolar(tnoon)
'    Dim solarDec As Double = SunDeclination(tnoon)
'    Dim hourAngle As Double = SunriseHourAngle(latitude, solarDec)

'    Dim delta As Double = longitude - Degrees(hourAngle)
'    Dim timeDiff As Double = 4 * delta
'    ' in minutes of time
'    Dim timeUTC As Double = 720 + timeDiff - eqTime
'    ' in minutes
'    ' alert("eqTime = " + eqTime + "\nsolarDec = " + solarDec + "\ntimeUTC = " + timeUTC);

'    ' *** Second pass includes fractional julianay in gamma calc

'    Dim newt As Double = JulianCenturies(JulianDayFromJulianCentury(t) + timeUTC / 1440.0)
'    eqTime = TrueSolarToMeanSolar(newt)
'    solarDec = SunDeclination(newt)
'    hourAngle = SunriseHourAngle(latitude, solarDec)
'    delta = longitude - Degrees(hourAngle)
'    timeDiff = 4 * delta
'    timeUTC = 720 + timeDiff - eqTime
'    ' in minutes
'    ' alert("eqTime = " + eqTime + "\nsolarDec = " + solarDec + "\ntimeUTC = " + timeUTC);

'    Return timeUTC
'End Function

'***********************************************************************/
'* Name: SolarNoonUTC   
'* Type: Function   
'* Purpose: calculate the Universal Coordinated Time (UTC) of solar 
'*   noon for the given day at the given location on earth  
'* Arguments:   
'* t : number of Julian centuries since J2000.0 
'* longitude : longitude of observer in degrees 
'* Return value:    
'* time in minutes from zero Z  
'***********************************************************************/

Public Function SolarNoonUTC(t As Double, longitude As Double) As Double
    ' First pass uses approximate solar noon to calculate eqtime
    Dim tnoon As Double = JulianCenturies(JulianDayFromJulianCentury(t) + longitude / 360.0)
    Dim eqTime As Double = TrueSolarToMeanSolar(tnoon)
    Dim solNoonUTC As Double = 720 + (longitude * 4) - eqTime
    ' min
    Dim newt As Double = JulianCenturies(JulianDayFromJulianCentury(t) - 0.5 + solNoonUTC / 1440.0)

    eqTime = TrueSolarToMeanSolar(newt)
    ' double solarNoonDec = SunDeclination(newt);
    solNoonUTC = 720 + (longitude * 4) - eqTime
    ' min
    Return solNoonUTC
End Function

'***********************************************************************/
'* Name: SunSetUTC  
'* Type: Function   
'* Purpose: calculate the Universal Coordinated Time (UTC) of sunset    
'*   for the given day at the given location on earth   
'* Arguments:   
'* julian : julian day  
'* latitude : latitude of observer in degrees   
'* longitude : longitude of observer in degrees 
'* Return value:    
'* time in minutes from zero Z  
'***********************************************************************/

Public Function SunSetUTC(julian As Double, latitude As Double, longitude As Double) As Double
    Dim t = JulianCenturies(julian)
    Dim eqTime = TrueSolarToMeanSolar(t)
    Dim solarDec = SunDeclination(t)
    Dim hourAngle = SunriseHourAngle(latitude, solarDec)
    hourAngle = -hourAngle
    Dim delta = longitude + Degrees(hourAngle)
    Dim timeUTC = 720 - (4.0 * delta) - eqTime
    ' in minutes
    Return timeUTC
End Function

Public Function SunRiseUTC(julian As Double, latitude As Double, longitude As Double) As Double
    Dim t = JulianCenturies(julian)
    Dim eqTime = TrueSolarToMeanSolar(t)
    Dim solarDec = SunDeclination(t)
    Dim hourAngle = SunriseHourAngle(latitude, solarDec)
    Dim delta = longitude + Degrees(hourAngle)
    Dim timeUTC = 720 - (4.0 * delta) - eqTime
    ' in minutes
    Return timeUTC
End Function

Public Function getTimeString(time As Double, timezone As Integer, julian As Double, dst As Boolean) As String
    Dim timeLocal = time + (timezone * 60.0)
    Dim riseT = JulianCenturies(julian + time / 1440.0)
    timeLocal += (If((dst), 60.0, 0.0))
    Return getTimeString(timeLocal)
End Function

Public Function getDateTime(time As Double, timezone As Integer, [date] As DateTime, dst As Boolean) As System.Nullable(Of DateTime)
    Dim julian As Double = JulianDay([date])
    Dim timeLocal = time + (timezone * 60.0)
    Dim riseT = JulianCenturies(julian + time / 1440.0)
    timeLocal += (If((dst), 60.0, 0.0))
    Return getDateTime(timeLocal, [date])
End Function

Private Function getTimeString(minutes As Double) As String

    Dim output As String = ""

    If (minutes >= 0) AndAlso (minutes < 1440) Then
        Dim floatHour = minutes / 60.0
        Dim hour = Math.Floor(floatHour)
        Dim floatMinute = 60.0 * (floatHour - Math.Floor(floatHour))
        Dim minute = Math.Floor(floatMinute)
        Dim floatSec = 60.0 * (floatMinute - Math.Floor(floatMinute))
        Dim second = Math.Floor(floatSec + 0.5)
        If second > 59 Then
            second = 0
            minute += 1
        End If
        If (second >= 30) Then
            minute += 1
        End If
        If minute > 59 Then
            minute = 0
            hour += 1
        End If
        output = [String].Format("{0:00}:{1:00}", hour, minute)
    Else
        Return "error"
    End If

    Return output
End Function

Private Function getDateTime(minutes As Double, [date] As DateTime) As System.Nullable(Of DateTime)

    Dim retVal As System.Nullable(Of DateTime) = Nothing

    If (minutes >= 0) AndAlso (minutes < 1440) Then
        Dim floatHour = minutes / 60.0
        Dim hour = Math.Floor(floatHour)
        Dim floatMinute = 60.0 * (floatHour - Math.Floor(floatHour))
        Dim minute = Math.Floor(floatMinute)
        Dim floatSec = 60.0 * (floatMinute - Math.Floor(floatMinute))
        Dim second = Math.Floor(floatSec + 0.5)
        If second > 59 Then
            second = 0
            minute += 1
        End If
        If (second >= 30) Then
            minute += 1
        End If
        If minute > 59 Then
            minute = 0
            hour += 1
        End If
        Return New DateTime([date].Year, [date].Month, [date].Day, CInt(hour), CInt(minute), CInt(second))
    Else
        Return retVal
    End If
End Function
End Module

Answer 5

This API seems to work for me:

http://sunrise-sunset.org/api

Answer 6

If you prefer an external service you could use this nice and free sunrise and sunset times API: http://sunrise-sunset.org/api

I have been using it for several projects and it works very well, data seems to be very accurate. Just do an HTTP GET request to http://api.sunrise-sunset.org/json

Accepted Parameters:

• lat: Latitude in decimal degrees. Required.
• lng: Longitude in decimal degrees. Required.
• date: Date in YYYY-MM-DD format. Also accepts other date formats and even relative date formats. If not present, date defaults to current date. Optional.
• callback: Callback function name for JSONP response. Optional.
• formatted: 0 or 1 (1 is default). Time values in response will be expressed following ISO 8601 and day_length will be expressed in seconds. Optional.

The response includes sunrise and sunset times as well as twilight times.

Answer 7

You need a formula which includes the equation of time to allow for the eccentric orbit of the Earth moon system around the sun. You need to use coordinates with proper datum points such as WGS84 or NAD27 or something like that. You need to use the JULIAN calendar and not the one we use on a daily basis to get5 these times right. It is not an easy thing to guess within a second of time. Id like to have the time at my location where the shadow length is equal to the whatever height. this should happen twice per day when the sun is elevated 60 degrees above the horizon before and after high noon. Also, as far as I understand, you just need to add exactly one day per year to get sidereal time so if you like increase your clock frequency X 366.25/365.25 you might now have a sidereal clock instead of a civil clock ??? "MATH is the LANGUAGE in which someone powerful has written the universe"

Answer 8

Start with this info:

Sunrise_equation

I'm using this to wright a ruby script that is still in the making. I'm having trouble understanding the multi-part julian dates.

One thing that is clear is that you should go for exact solar transit time. Then subtract and add the semi_diurnal_arc = acos(cos_omega) which is based upon your latitude and the solar declination. Oh! And be sure to include solar center and earth refraction. It seems this earth is quite the magician.