public static double Calc(JulianDayNumber julianDay, double tidalAcceleration)
{
var gregorianYear = julianDay.GetGregorianYear();
double dt = 0.0;
if (julianDay >= J2016 || julianDay < JMinus720)
{
var t = (gregorianYear - 1825) / 100.0;
dt = -320 + 32.5 * t * t;
if (julianDay >= J2016)
{
dt += 269.4790417; // to make curve continous on 1 Jan 2016 (D. Koch)
}
else
{
dt -= 179.7337208; // to make curve continous on 1 Jan -720 (D. Koch)
}
}
else
{
for (int i = 0; i < _coefficients.Length; i++)
{
ref var data = ref _coefficients[i];
if (julianDay < data.End)
{
var t = (double)(julianDay - data.Begin) / (double)(data.End - data.Begin);
dt = data.Coef1 + data.Coef2 * t + data.Coef3 * t * t + data.Coef4 * t * t * t;
}
}
}
/// <see cref="deltat_longterm_morrison_stephenson"/>
public static double Calc(JulianDayNumber tjd)
{
var gregorianYear = tjd.GetGregorianYear();
double u = (gregorianYear - 1820) / 100.0;
return(-20 + 32 * u * u);
}
/// <summary>
/// Stephenson & Morrison (2004)
/// </summary>
public static double Calc(JulianDayNumber tjd, double tid_acc)
{
double ans = 0, ans2, ans3;
double p, B, dd;
double tjd0;
int iy;
double Y = tjd.GetGregorianYear();
/* before -1000:
* formula by Stephenson & Morrison (2004; p. 335) but adjusted to fit the
* starting point of table dt2. */
if (Y < DeltaTTabulated.Tab2Start)
{
// before -1000
ans = DeltaTLongtermMorrisonStephenson.Calc(tjd);
ans = TidalAcceleration.AdjustForTidalAcceleration(ans, Y, tid_acc, TidalAccelerationMode.Const26, false);
/* transition from formula to table over 100 years */
if (Y >= DeltaTTabulated.Tab2Start - 100)
{
/* starting value of table dt2: */
ans2 = TidalAcceleration.AdjustForTidalAcceleration(DeltaTTabulated.dt2[0], DeltaTTabulated.Tab2Start, tid_acc, TidalAccelerationMode.Const26, false);
/* value of formula at epoch TAB2_START */
/* B = (TAB2_START - LTERM_EQUATION_YSTART) * 0.01;
* ans3 = -20 + LTERM_EQUATION_COEFF * B * B;*/
tjd0 = (DeltaTTabulated.Tab2Start - 2000) * 365.2425 + (double)JulianDayNumber.J2000;
ans3 = DeltaTLongtermMorrisonStephenson.Calc(JulianDayNumber.FromRaw(tjd0));
ans3 = TidalAcceleration.AdjustForTidalAcceleration(ans3, Y, tid_acc, TidalAccelerationMode.Const26, false);
dd = ans3 - ans2;
B = (Y - (DeltaTTabulated.Tab2Start - 100)) * 0.01;
/* fit to starting point of table dt2. */
ans -= dd * B;
}
}
/* between -1000 and 1600:
* linear interpolation between values of table dt2 (Stephenson & Morrison 2004) */
if (Y >= DeltaTTabulated.Tab2Start && Y < DeltaTTabulated.Tab2End)
{
double Yjul = tjd.GetJulianYear();
p = Math.Floor(Yjul);
iy = (int)((p - DeltaTTabulated.Tab2Start) / DeltaTTabulated.Tab2Step);
dd = (Yjul - (DeltaTTabulated.Tab2Start + DeltaTTabulated.Tab2Step * iy)) / DeltaTTabulated.Tab2Step;
ans = DeltaTTabulated.dt2[iy] + (DeltaTTabulated.dt2[iy + 1] - DeltaTTabulated.dt2[iy]) * dd;
/* correction for tidal acceleration used by our ephemeris */
ans = TidalAcceleration.AdjustForTidalAcceleration(ans, Y, tid_acc, TidalAccelerationMode.Const26, false);
}
ans /= 86400.0;
return(ans);
}
/// <summary>
/// Model used SE 1.77 - 2.05.01, for epochs before 1633:
/// Polynomials by Espenak & Meeus 2006, derived from Stephenson & Morrison 2004.
/// deltat_model == SEMOD_DELTAT_ESPENAK_MEEUS_2006:
/// This method is used only for epochs before 1633.
/// (For more recent epochs, we use the data provided by Astronomical Almanac K8-K9.)
/// </summary>
/// <see cref="deltat_espenak_meeus_1620"/>
public static double Calc(JulianDayNumber tjd, double tidalAcceleration)
{
double ans = 0;
double u;
double Ygreg = tjd.GetGregorianYear();
if (Ygreg < -500)
{
ans = DeltaTLongtermMorrisonStephenson.Calc(tjd);
}
else if (Ygreg < 500)
{
u = Ygreg / 100.0;
ans = (((((0.0090316521 * u + 0.022174192) * u - 0.1798452) * u - 5.952053) * u + 33.78311) * u - 1014.41) * u + 10583.6;
}
else if (Ygreg < 1600)
{
u = (Ygreg - 1000) / 100.0;
ans = (((((0.0083572073 * u - 0.005050998) * u - 0.8503463) * u + 0.319781) * u + 71.23472) * u - 556.01) * u + 1574.2;
}
else if (Ygreg < 1700)
{
u = Ygreg - 1600;
ans = 120 - 0.9808 * u - 0.01532 * u * u + u * u * u / 7129.0;
}
else if (Ygreg < 1800)
{
u = Ygreg - 1700;
ans = (((-u / 1174000.0 + 0.00013336) * u - 0.0059285) * u + 0.1603) * u + 8.83;
}
else if (Ygreg < 1860)
{
u = Ygreg - 1800;
ans = ((((((0.000000000875 * u - 0.0000001699) * u + 0.0000121272) * u - 0.00037436) * u + 0.0041116) * u + 0.0068612) * u - 0.332447) * u + 13.72;
}
else if (Ygreg < 1900)
{
u = Ygreg - 1860;
ans = ((((u / 233174.0 - 0.0004473624) * u + 0.01680668) * u - 0.251754) * u + 0.5737) * u + 7.62;
}
else if (Ygreg < 1920)
{
u = Ygreg - 1900;
ans = (((-0.000197 * u + 0.0061966) * u - 0.0598939) * u + 1.494119) * u - 2.79;
}
else if (Ygreg < 1941)
{
u = Ygreg - 1920;
ans = 21.20 + 0.84493 * u - 0.076100 * u * u + 0.0020936 * u * u * u;
}
else if (Ygreg < 1961)
{
u = Ygreg - 1950;
ans = 29.07 + 0.407 * u - u * u / 233.0 + u * u * u / 2547.0;
}
else if (Ygreg < 1986)
{
u = Ygreg - 1975;
ans = 45.45 + 1.067 * u - u * u / 260.0 - u * u * u / 718.0;
}
else if (Ygreg < 2005)
{
u = Ygreg - 2000;
ans = ((((0.00002373599 * u + 0.000651814) * u + 0.0017275) * u - 0.060374) * u + 0.3345) * u + 63.86;
}
ans = TidalAcceleration.AdjustForTidalAcceleration(ans, Ygreg, tidalAcceleration, TidalAccelerationMode.Const26, false);
ans /= 86400.0;
return(ans);
}
/// <summary>
/// Calculate DeltaT
/// </summary>
/// <remarks>
/// delta t is adjusted to the tidal acceleration that is compatible
/// with the ephemeris mode contained in ephemerisMode and with the ephemeris
/// files made accessible through swe_set_ephe_path() or swe_set_jplfile().
/// If ephemerisMode is null, then the default tidal acceleration is ussed(i.e. that of DE431).
/// </remarks>
/// <see cref="calc_deltat"/>
/// <returns>DeltaT (ET - UT) in days</returns>
public static double Calc(JulianDayNumber julianDay, DeltaTMode deltaTMode, EphemerisMode?ephemerisMode)
{
var tidalAcceleration = ephemerisMode is null
? TidalAcceleration.Get(JPLDENumber.Default)
: TidalAcceleration.Calculate(ephemerisMode.Value, julianDay, JPLDENumber.Auto);
if (deltaTMode == DeltaTMode.Stephenson_Etc_2016 && julianDay < JulianDayNumber.J1955)
{
double deltaT = DeltaTStephensonEtc2016.Calc(julianDay, tidalAcceleration);
if (julianDay >= JulianDayNumber.J1952_05_04)
{
deltaT += (1.0 - (double)(JulianDayNumber.J1955 - julianDay) / 1000.0) * 0.6610218 / 86400.0;
}
return(deltaT);
}
if (deltaTMode == DeltaTMode.Espenak_Meeus_2006 && julianDay < J1633)
{
return(DeltaTEspenakMeeus1620.Calc(julianDay, tidalAcceleration));
}
var year = julianDay.GetYear();
// delta t model used in SE 1.72 - 1.76: Stephenson & Morrison 2004; before 1620
if (deltaTMode == DeltaTMode.Stephenson_Morrison_2004 && year < DeltaTTabulated.TabStart)
{
// before 1600:
if (year < DeltaTTabulated.Tab2End)
{
return(DeltaTStephensonMorrison2004_1600.Calc(julianDay, tidalAcceleration));
}
else
{
// between 1600 and 1620:
// linear interpolation between end of table dt2 and start of table dt
return(DeltaTTabulated.CalcInterpolated(year, julianDay.GetGregorianYear(), tidalAcceleration));
}
}
/* delta t model used before SE 1.64:
* Stephenson/Morrison 1984 with Borkowski 1988;
* before 1620 */
if (deltaTMode == DeltaTMode.Stephenson_Morrison_1984 && year < DeltaTTabulated.TabStart)
{
double B;
double ans;
if (year >= 948.0)
{
/* Stephenson and Morrison, stated domain is 948 to 1600:
* 25.5(centuries from 1800)^2 - 1.9159(centuries from 1955)^2 */
B = 0.01 * (year - 2000.0);
ans = (23.58 * B + 100.3) * B + 101.6;
}
else
{
/* Borkowski, before 948 and between 1600 and 1620 */
B = 0.01 * (year - 2000.0) + 3.75;
ans = 35.0 * B * B + 40.0;
}
return(ans / 86400.0);
}
/* 1620 - today + a few years (tabend):
* Tabulated values of deltaT from Astronomical Almanac
* (AA 1997etc., pp. K8-K9) and from IERS
* (http://maia.usno.navy.mil/ser7/deltat.data).
*/
if (year >= DeltaTTabulated.TabStart)
{
return(DeltaTTabulated.Calc(julianDay, tidalAcceleration, deltaTMode));
}
return(0);
}