aper13¶
- erfa.aper13(ut11, ut12, astrom)[source]¶
In the star-independent astrometry parameters, update only the Earth rotation angle.
- Parameters:
- ut11double array
- ut12double array
- astromeraASTROM array
- Returns:
- astromeraASTROM array
Notes
Wraps ERFA function
eraAper13. Note that, unlike the erfa routine, the python wrapper does not change astrom in-place. The ERFA documentation is:- - - - - - - - - - e r a A p e r 1 3 - - - - - - - - - - In the star-independent astrometry parameters, update only the Earth rotation angle. The caller provides UT1, (n.b. not UTC). Given: ut11 double UT1 as a 2-part... ut12 double ...Julian Date (Note 1) astrom eraASTROM star-independent astrometry parameters: pmt double not used eb double[3] not used eh double[3] not used em double not used v double[3] not used bm1 double not used bpn double[3][3] not used along double longitude + s' (radians) xpl double not used ypl double not used sphi double not used cphi double not used diurab double not used eral double not used refa double not used refb double not used Returned: astrom eraASTROM star-independent astrometry parameters: pmt double unchanged eb double[3] unchanged eh double[3] unchanged em double unchanged v double[3] unchanged bm1 double unchanged bpn double[3][3] unchanged along double unchanged xpl double unchanged ypl double unchanged sphi double unchanged cphi double unchanged diurab double unchanged eral double "local" Earth rotation angle (radians) refa double unchanged refb double unchanged Notes: 1) The UT1 date (n.b. not UTC) ut11+ut12 is a Julian Date, apportioned in any convenient way between the arguments ut11 and ut12. For example, JD(UT1)=2450123.7 could be expressed in any of these ways, among others: ut11 ut12 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 and MJD methods are good compromises between resolution and convenience. The date & time method is best matched to the algorithm used: maximum precision is delivered when the ut11 argument is for 0hrs UT1 on the day in question and the ut12 argument lies in the range 0 to 1, or vice versa. 2) If the caller wishes to provide the Earth rotation angle itself, the function eraAper can be used instead. One use of this technique is to substitute Greenwich apparent sidereal time and thereby to support equinox based transformations directly. 3) This is one of several functions that inserts into the astrom structure star-independent parameters needed for the chain of astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed. The various functions support different classes of observer and portions of the transformation chain: functions observer transformation eraApcg eraApcg13 geocentric ICRS <-> GCRS eraApci eraApci13 terrestrial ICRS <-> CIRS eraApco eraApco13 terrestrial ICRS <-> observed eraApcs eraApcs13 space ICRS <-> GCRS eraAper eraAper13 terrestrial update Earth rotation eraApio eraApio13 terrestrial CIRS <-> observed Those with names ending in "13" use contemporary ERFA models to compute the various ephemerides. The others accept ephemerides supplied by the caller. The transformation from ICRS to GCRS covers space motion, parallax, light deflection, and aberration. From GCRS to CIRS comprises frame bias and precession-nutation. From CIRS to observed takes account of Earth rotation, polar motion, diurnal aberration and parallax (unless subsumed into the ICRS <-> GCRS transformation), and atmospheric refraction. Called: eraAper astrometry parameters: update ERA eraEra00 Earth rotation angle, IAU 2000 This revision: 2013 September 25 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.