Transform star RA,Dec from geocentric CIRS to ICRS astrometric using the SOFA Atic13 function.

Namespace: ASCOM.Astrometry.SOFA
Assembly: ASCOM.Astrometry (in ASCOM.Astrometry.dll) Version: 6.0.0.0 (6.1.1.2619)

Syntax

C#
public void IntermediateToCelestial(
	double ri,
	double di,
	double date1,
	double date2,
	ref double rc,
	ref double dc,
	ref double eo
)
Visual Basic
Public Sub IntermediateToCelestial ( _
	ri As Double, _
	di As Double, _
	date1 As Double, _
	date2 As Double, _
	ByRef rc As Double, _
	ByRef dc As Double, _
	ByRef eo As Double _
)
Visual C++
public:
virtual void IntermediateToCelestial(
	double ri, 
	double di, 
	double date1, 
	double date2, 
	double% rc, 
	double% dc, 
	double% eo
) sealed

Parameters

ri
Type: System..::..Double
CIRS geocentric RA (radians)
di
Type: System..::..Double
CIRS geocentric Dec (radians)
date1
Type: System..::..Double
TDB as a 2-part Julian Date (Note 1)
date2
Type: System..::..Double
TDB as a 2-part Julian Date (Note 1)
rc
Type: System..::..Double%
ICRS astrometric RA (radians)
dc
Type: System..::..Double%
ICRS astrometric Dec (radians)
eo
Type: System..::..Double%
equation of the origins (ERA-GST, Note 4)

Remarks

Notes:
  1. The TDB date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TDB)=2450123.8g could be expressed in any of these ways, among others:
    Date 1Date 2Method
    2450123.8 0.0 JD method
    2451545.0 -1421.3 J2000 method
    2400000.5 50123.2 MJD method
    2450123.5 0.2 Date and time method

    The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date and time methods are both good compromises between resolution and convenience. For most applications of this function the choice will not be at all critical.

    TT can be used instead of TDB without any significant impact on accuracy.

  2. Iterative techniques are used for the aberration and light deflection corrections so that the functions Atic13 and Atci13 are accurate inverses; even at the edge of the Sun's disk the discrepancy is only about 1 nanoarcsecond.
  3. The available accuracy is better than 1 milliarcsecond, limited mainly by the precession-nutation model that is used, namely IAU 2000A/2006. Very close to solar system bodies, additional errors of up to several milliarcseconds can occur because of unmodeled light deflection; however, the Sun's contribution is taken into account, to first order. The accuracy limitations of the SOFA function iauEpv00 (used to compute Earth position and velocity) can contribute aberration errors of up to 5 microarcseconds. Light deflection at the Sun's limb is uncertain at the 0.4 mas level.
  4. Should the transformation to (equinox based) J2000.0 mean place be required rather than (CIO based) ICRS coordinates, subtract the equation of the origins from the returned right ascension: RA = RI - EO. (The Anp function can then be applied, as required, to keep the result in the conventional 0-2pi range.)

See Also