atic13¶
- erfa.atic13(ri, di, date1, date2)[source]¶
Transform star RA,Dec from geocentric CIRS to ICRS astrometric.
- Parameters:
- ridouble array
- didouble array
- date1double array
- date2double array
- Returns:
- rcdouble array
- dcdouble array
- eodouble array
Notes
Wraps ERFA function
eraAtic13
. The ERFA documentation is:- - - - - - - - - - e r a A t i c 1 3 - - - - - - - - - - Transform star RA,Dec from geocentric CIRS to ICRS astrometric. Given: ri,di double CIRS geocentric RA,Dec (radians) date1 double TDB as a 2-part... date2 double ...Julian Date (Note 1) Returned: rc,dc double ICRS astrometric RA,Dec (radians) eo double equation of the origins (ERA-GST, radians, Note 4) Notes: 1) The TDB date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TDB)=2450123.7 could be expressed in any of these ways, among others: date1 date2 2450123.7 0.0 (JD method) 2451545.0 -1421.3 (J2000 method) 2400000.5 50123.2 (MJD method) 2450123.5 0.2 (date & 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 & 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 eraAtic13 (or eraAticq) and eraAtci13 (or eraAtciq) 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 ERFA function eraEpv00 (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 eraAnp function can then be applied, as required, to keep the result in the conventional 0-2pi range.) Called: eraApci13 astrometry parameters, ICRS-CIRS, 2013 eraAticq quick CIRS to ICRS astrometric This revision: 2022 May 3 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.