日出日落是可以根据经度纬度计算出来的，这里有一个现成代码的公共类库，复制下来作为一个类文件就可以调用了。一般不需要了解实现过程，各种数学公式太麻烦。
调用方法：.
SunTimeResult result = SunTimes.GetSunTime(DateTime.Now, double.Parse(Longitude), double.Parse(Latitude));MessageBox.Show(string.Format("今天日出时间:{0},日落时间:{1}", result.SunriseTime.ToString("HH:mm:ss"), result.SunsetTime.ToString("HH:mm:ss")));
DateTime.Now是现在的时间
Longitude是经度
Latitude是纬度
类库代码如下：
using System;namespace SwitchTime{/// <summary>/// 日出日落时间类/// </summary>public static class SunTimes{#region 公共方法/// <summary>/// 计算日长/// </summary>/// <param name="date">日期</param>/// <param name="longitude">经度</param>/// <param name="latitude">纬度</param>/// <returns>日长</returns>/// <remarks>/// 注：日期最小为2000.1.1号/// </remarks>public static double GetDayLength(DateTime date, double longitude, double latitude){double result = DayLen(date.Year, date.Month, date.Day, longitude, latitude, -35.0 / 60.0, 1);return result;}/// <summary>/// 计算日出日没时间/// </summary>/// <param name="date">日期</param>/// <param name="longitude">经度</param>/// <param name="latitude">纬度</param>/// <returns>日落日出时间</returns>/// <remarks>/// 注：日期最小为2000.1.1号/// </remarks>public static SunTimeResult GetSunTime(DateTime date, double longitude, double latitude){double start = 0;double end = 0;SunRiset(date.Year, date.Month, date.Day, longitude, latitude, -35.0 / 60.0, 1, ref start, ref end);DateTime sunrise = ToLocalTime(date, start);DateTime sunset = ToLocalTime(date, end);return new SunTimeResult(sunrise, sunset);}#endregion#region 私有方法#region 时间转换private static DateTime ToLocalTime(DateTime time, double utTime){int hour = Convert.ToInt32(Math.Floor(utTime));double temp = utTime - hour;hour += 8;//转换为东8区北京时间temp = temp * 60;int minute = Convert.ToInt32(Math.Floor(temp));try{return new DateTime(time.Year, time.Month, time.Day, hour, minute, 0);}catch{return new DateTime(time.Year, time.Month, time.Day, 0, 0, 0);}}#endregion#region 与日出日落时间相关计算private static double DayLen(int year, int month, int day, double lon, double lat,double altit, int upper_limb){double d, /* Days since 2000 Jan 0.0 (negative before) */obl_ecl, /* Obliquity (inclination) of Earth's axis *///黄赤交角，在2000.0历元下国际规定为23度26分21.448秒，但有很小的时间演化。sr, /* Solar distance, astronomical units */slon, /* True solar longitude */sin_sdecl, /* Sine of Sun's declination *///太阳赤纬的正弦值。cos_sdecl, /* Cosine of Sun's declination */sradius, /* Sun's apparent radius */t; /* Diurnal arc *//* Compute d of 12h local mean solar time */d = Days_since_2000_Jan_0(year, month, day) + 0.5 - lon / 360.0;/* Compute obliquity of ecliptic (inclination of Earth's axis) */obl_ecl = 23.4393 - 3.563E-7 * d;//这个黄赤交角时变公式来历复杂，很大程度是经验性的，不必追究。/* Compute Sun's position */slon = 0.0;sr = 0.0;Sunpos(d, ref slon, ref sr);/* Compute sine and cosine of Sun's declination */sin_sdecl = Sind(obl_ecl) * Sind(slon);cos_sdecl = Math.Sqrt(1.0 - sin_sdecl * sin_sdecl);//用球面三角学公式计算太阳赤纬。/* Compute the Sun's apparent radius, degrees */sradius = 0.2666 / sr;//视半径，同前。/* Do correction to upper limb, if necessary */if (upper_limb != 0)altit -= sradius;/* Compute the diurnal arc that the Sun traverses to reach *//* the specified altitide altit: *///根据设定的地平高度判据计算周日弧长。double cost;cost = (Sind(altit) - Sind(lat) * sin_sdecl) /(Cosd(lat) * cos_sdecl);if (cost >= 1.0)t = 0.0; /* Sun always below altit *///极夜。else if (cost <= -1.0)t = 24.0; /* Sun always above altit *///极昼。else t = (2.0 / 15.0) * Acosd(cost); /* The diurnal arc, hours *///周日弧换算成小时计。return t;}private static void Sunpos(double d, ref double lon, ref double r){double M,//太阳的平均近点角，从太阳观察到的地球（=从地球看到太阳的）距近日点（近地点）的角度。w, //近日点的平均黄道经度。e, //地球椭圆公转轨道离心率。E, //太阳的偏近点角。计算公式见下面。x, y,v; //真近点角，太阳在任意时刻的真实近点角。M = Revolution(356.0470 + 0.9856002585 * d);//自变量的组成：2000.0时刻太阳黄经为356.0470度,此后每天约推进一度（360度/365天w = 282.9404 + 4.70935E-5 * d;//近日点的平均黄经。e = 0.016709 - 1.151E-9 * d;//地球公转椭圆轨道离心率的时间演化。以上公式和黄赤交角公式一样，不必深究。E = M + e * Radge * Sind(M) * (1.0 + e * Cosd(M));x = Cosd(E) - e;y = Math.Sqrt(1.0 - e * e) * Sind(E);r = Math.Sqrt(x * x + y * y);v = Atan2d(y, x);lon = v + w;if (lon >= 360.0)lon -= 360.0;}private static void Sun_RA_dec(double d, ref double RA, ref double dec, ref double r){double lon, obl_ecl, x, y, z;lon = 0.0;Sunpos(d, ref lon, ref r);//计算太阳的黄道坐标。x = r * Cosd(lon);y = r * Sind(lon);//计算太阳的直角坐标。obl_ecl = 23.4393 - 3.563E-7 * d;//黄赤交角，同前。z = y * Sind(obl_ecl);y = y * Cosd(obl_ecl);//把太阳的黄道坐标转换成赤道坐标（暂改用直角坐标）。RA = Atan2d(y, x);dec = Atan2d(z, Math.Sqrt(x * x + y * y));//最后转成赤道坐标。显然太阳的位置是由黄道坐标方便地直接确定的，但必须转换到赤//道坐标里才能结合地球的自转确定我们需要的白昼长度。}/// <summary>/// 日出没时刻计算/// </summary>/// <param name="year">年</param>/// <param name="month">月</param>/// <param name="day">日</param>/// <param name="lon"></param>/// <param name="lat"></param>/// <param name="altit"></param>/// <param name="upper_limb"></param>/// <param name="trise">日出时刻</param>/// <param name="tset">日没时刻</param>/// <returns>太阳有出没现象，返回0 极昼，返回+1 极夜，返回-1</returns>private static int SunRiset(int year, int month, int day, double lon, double lat,double altit, int upper_limb, ref double trise, ref double tset){double d, /* Days since 2000 Jan 0.0 (negative before) *///以历元2000.0起算的日数。sr, /* Solar distance, astronomical units *///太阳距离，以天文单位计算（约1.5亿公里）。sRA, /* Sun's Right Ascension *///同前，太阳赤经。sdec, /* Sun's declination *///太阳赤纬。sradius, /* Sun's apparent radius *///太阳视半径，约16分（受日地距离、大气折射等诸多影响）t, /* Diurnal arc *///周日弧，太阳一天在天上走过的弧长。tsouth, /* Time when Sun is at south */sidtime; /* Local sidereal time *///当地恒星时，即地球的真实自转周期。比平均太阳日（日常时间）长3分56秒。int rc = 0; /* Return cde from function - usually 0 *//* Compute d of 12h local mean solar time */d = Days_since_2000_Jan_0(year, month, day) + 0.5 - lon / 360.0;//计算观测地当日中午时刻对应2000.0起算的日数。/* Compute local sideral time of this moment */sidtime = Revolution(GMST0(d) + 180.0 + lon);//计算同时刻的当地恒星时（以角度为单位）。以格林尼治为基准，用经度差校正。/* Compute Sun's RA + Decl at this moment */sRA = 0.0;sdec = 0.0;sr = 0.0;Sun_RA_dec(d, ref sRA, ref sdec, ref sr);//计算同时刻太阳赤经赤纬。/* Compute time when Sun is at south - in hours UT */tsouth = 12.0 - Rev180(sidtime - sRA) / 15.0;//计算太阳日的正午时刻，以世界时（格林尼治平太阳时）的小时计。/* Compute the Sun's apparent radius, degrees */sradius = 0.2666 / sr;//太阳视半径。0.2666是一天文单位处的太阳视半径（角度）。/* Do correction to upper limb, if necessary */if (upper_limb != 0)altit -= sradius;//如果要用上边缘，就要扣除一个视半径。/* Compute the diurnal arc that the Sun traverses to reach *///计算周日弧。直接利用球面三角公式。如果碰到极昼极夜问题，同前处理。/* the specified altitide altit: */double cost;cost = (Sind(altit) - Sind(lat) * Sind(sdec)) /(Cosd(lat) * Cosd(sdec));if (cost >= 1.0){rc = -1;t = 0.0;}else{if (cost <= -1.0){rc = +1;t = 12.0; /* Sun always above altit */}elset = Acosd(cost) / 15.0; /* The diurnal arc, hours */}/* Store rise and set times - in hours UT */trise = tsouth - t;tset = tsouth + t;return rc;}#endregion#region 辅助函数/// <summary>/// 历元2000.0，即以2000年第一天开端为计日起始（天文学以第一天为0日而非1日）。/// 它与UT（就是世界时，格林尼治平均太阳时）1999年末重合。/// </summary>/// <param name="y"></param>/// <param name="m"></param>/// <param name="d"></param>/// <returns></returns>private static long Days_since_2000_Jan_0(int y, int m, int d){return (367L * (y) - ((7 * ((y) + (((m) + 9) / 12))) / 4) + ((275 * (m)) / 9) + (d) - 730530L);}private static double Revolution(double x){return (x - 360.0 * Math.Floor(x * Inv360));}private static double Rev180(double x){return (x - 360.0 * Math.Floor(x * Inv360 + 0.5));}private static double GMST0(double d){double sidtim0;sidtim0 = Revolution((180.0 + 356.0470 + 282.9404) +(0.9856002585 + 4.70935E-5) * d);return sidtim0;}private static double Inv360 = 1.0 / 360.0;#endregion#region 度与弧度转换系数，为球面三角计算作准备private static double Sind(double x){return Math.Sin(x * Degrad);}private static double Cosd(double x){return Math.Cos(x * Degrad);}private static double Tand(double x){return Math.Tan(x * Degrad);}private static double Atand(double x){return Radge * Math.Atan(x);}private static double Asind(double x){return Radge * Math.Asin(x);}private static double Acosd(double x){return Radge * Math.Acos(x);}private static double Atan2d(double y, double x){return Radge * Math.Atan2(y, x);}private static double Radge = 180.0 / Math.PI;private static double Degrad = Math.PI / 180.0;#endregion#endregion}/// <summary>/// 日出日落时间结果/// </summary>public class SunTimeResult{#region 构造与析构/// <summary>/// 构造函数/// </summary>/// <param name="sunrise">日出时间</param>/// <param name="sunset">日落时间</param>public SunTimeResult(DateTime sunrise, DateTime sunset){sunriseTime = sunrise;sunsetTime = sunset;}#endregion#region 属性定义/// <summary>/// 获取日出时间/// </summary>public DateTime SunriseTime{get{return sunriseTime;}}/// <summary>/// 获取日落时间/// </summary>public DateTime SunsetTime{get{return sunsetTime;}}#endregion#region 私成员private DateTime sunriseTime;//日出时间private DateTime sunsetTime;//日落时间#endregion}}
