atci13¶
- erfa.atci13(rc, dc, pr, pd, px, rv, date1, date2)[source]¶
Transform ICRS star data, epoch J2000.0, to CIRS.
- Parameters:
- rcdouble array
- dcdouble array
- prdouble array
- pddouble array
- pxdouble array
- rvdouble array
- date1double array
- date2double array
- Returns:
- ridouble array
- didouble array
- eodouble array
Notes
Wraps ERFA function
eraAtci13
. The ERFA documentation is:- - - - - - - - - - e r a A t c i 1 3 - - - - - - - - - - Transform ICRS star data, epoch J2000.0, to CIRS. Given: rc double ICRS right ascension at J2000.0 (radians, Note 1) dc double ICRS declination at J2000.0 (radians, Note 1) pr double RA proper motion (radians/year, Note 2) pd double Dec proper motion (radians/year) px double parallax (arcsec) rv double radial velocity (km/s, +ve if receding) date1 double TDB as a 2-part... date2 double ...Julian Date (Note 3) Returned: ri,di double* CIRS geocentric RA,Dec (radians) eo double* equation of the origins (ERA-GST, radians, Note 5) Notes: 1) Star data for an epoch other than J2000.0 (for example from the Hipparcos catalog, which has an epoch of J1991.25) will require a preliminary call to eraPmsafe before use. 2) The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt. 3) 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. 4) 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. 5) Should the transformation to (equinox based) apparent place be required rather than (CIO based) intermediate place, 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 eraAtciq quick ICRS to CIRS This revision: 2022 May 3 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.