/* Analysation of algorithm of Hồ Ngọc Đức
* ---------------------------------------
* double off = LocalToJD(31, 12, Y) - 2415021.076998695;
* ^ returns Julian Date of 31st December #Year, 00:00:00 UTC+7
* i.e. 30th December #Year, 17:00:00 UTC
* int k = INT(off / 29.530588853);
* double jd = NewMoon(k);
* ^ returns the new moon date *time* in Julian Dater, *UTC*
* int[] ret = LocalFromJD(jd);
* ^ converts (jd + timezone/24) back to Calendar Date,
* disregrading the time (i.e. the begining of day in local time zone
* [00:00:00 local] that contains the new moon.)
*
* // sun longitude at local midnight
* double sunLong = SunLongitude(LocalToJD(ret[0], ret[1], ret[2]));
* if (sunLong > 3 * PI / 2)
* {
* jd = NewMoon(k - 1);
* }
* return LocalFromJD(jd);
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* e.g.:
* NewMoon(1236) = 2451520.4393767994
* = 7/12/1999 10:32:42 UTC
* = 8/12/1999 17:32:42 UTC+7, thus,
*
* [ Note: UniversalFromJD(2451520.4393767994) = (7, 12, 1999) ]
* LocalFromJD(2451520.4393767994) =
* UniversalFromJD(JD + LOCAL_TIMEZONE/24.0) = (8, 12, 1999)
*
* LocalToJD(8, 12, 1999) =
* UniversalToJD(D, M, Y) - LOCAL_TIMEZONE/24.0 = 8/12/1999 00:00:00 - 7
* ^ ^ = 7/12/1999 17:00:00 UTC <---+
* | +---[ Shift back to local midnight ] |
* +---[ Julius Date of D/M/Y 00:00:00 UTC (midnight), 8/12/1999 00:00:00] |
* [ This value is used to determine the sun longitude ]---+
*/
/// <summary>
/// Returns the local date time of the new moon just before
/// the winter solstice in the given lunar year.
/// </summary>
/// <param name="lunarYear"></param>
/// <param name="timeZone"></param>
/// <returns></returns>
public static DateTime GetNewMoon11(int lunarYear, double timeZone)
{
// number of days from J1900 to local midnight of 31st December #Year
// (lunarYear, 12, 31): local
// (lunarYear, 12, 31, timeZone): universal
var offset = JulianDateConverter.UniversalDateTimeToJulianDate(lunarYear, 12, 31, timeZone) - Constants.J1900;
var k = (int)(offset / Constants.SynodicMonth);
// local date & *time* of new moon
var newMoonLocalDateTime = JulianDateConverter.JulianDateToUniversalDateTime(GetNewMoon(k)).AddHours(timeZone);
// beginning of that day (i.e. midnight, i.e. strip off the time)
var newMoonMidnightLocal = newMoonLocalDateTime.Date;
// Julian Date at the beginning of that day
var julianDate =
newMoonMidnightLocal.AddHours(-timeZone).UniversalDateTimeToJulianDate();
var sunLongitude = Sun.GetSunLongitudeAtJulianDate(julianDate);
// Check the winter solstice is after the beginning of that day:
// If the winter soltice is *before* the beginning of that day,
// the previous new moon is the new moon just before winter solstice,
// else the current new moon is the new moon just before winter solstice.
if (sunLongitude > (3 * Math.PI / 2))
{
newMoonLocalDateTime = JulianDateConverter.JulianDateToUniversalDateTime(GetNewMoon(k - 1)).AddHours(timeZone);
}
return(newMoonLocalDateTime);
}
public static int GetSolarTermIndex(DateTime dateTime)
{
var julianDate = JulianDateConverter.UniversalDateTimeToJulianDate(dateTime);
return((int)(GetSunLongitudeAtJulianDate(julianDate) / Math.PI * 12));
}