The Carrington Rotation Number is defined as the number of rotations which the Sun has done since 9 November 1853.
The time for one rotation of the Sun (in essence, one “day” on the Sun) is 27.2753 days.
The calculation is based on the fact that rotation 1690 started on 27 Dec 1979, so what it does is works out the number of days between that date and the date you want the CRN for, and divide by 27.2753, and then adding 1690.
public static double CalcCRN(DateTime dDate)
{
double fCRN;
double fJulian;
fJulian = UraniaTime.GetJulianDay(dDate, 0);
fCRN = 1690 + ((fJulian - 2444235.34)/27.2753);
return fCRN;
}
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