/// <summary>
/// Calculates the value of DeltaT using SOFA
/// Published DeltaT information: https://www.usno.navy.mil/USNO/earth-orientation/eo-products/long-term
/// Formula: deltaT = 32.184 + (TAI - UTC) - (UT1 - UTC) https://de.wikipedia.org/wiki/Delta_T
/// </summary>
/// <param name="date">Date to retrieve DeltaT for</param>
/// <returns>DeltaT at given date</returns>
public static double DeltaT(DateTime date)
{
var utcDate = date.ToUniversalTime();
double utc1 = 0, utc2 = 0, tai1 = 0, tai2 = 0;
SOFA.Dtf2d("UTC", utcDate.Year, utcDate.Month, utcDate.Day, utcDate.Hour, utcDate.Minute, (double)utcDate.Second + (double)utcDate.Millisecond / 1000.0, ref utc1, ref utc2);
SOFA.UtcTai(utc1, utc2, ref tai1, ref tai2);
var utc = utc1 + utc2;
var tai = tai1 + tai2;
var deltaT = 32.184 + DaysToSeconds((tai - utc)) - DeltaUT(utcDate);
return(deltaT);
}
public Coordinates Transform(Epoch epoch)
{
var now = DateTime.Now;
var jdUTC = Astrometry.GetJulianDate(now);
var zenithDistance = Astrometry.ToRadians(90d - Altitude.Degree);
var deltaUT = Astrometry.DeltaUT(now);
var raRad = 0d;
var decRad = 0d;
SOFA.TopocentricToCelestial("A", Azimuth.Radians, zenithDistance, jdUTC, 0d, deltaUT, Longitude.Radians, Latitude.Radians, 0d, 0d, 0d, 0d, 0d, 0d, 0d, ref raRad, ref decRad);
var ra = Angle.ByRadians(raRad);
var dec = Angle.ByRadians(decRad);
var coordinates = new Coordinates(ra, dec, Epoch.J2000);
return(coordinates.Transform(epoch));
}
