xys00a¶
- erfa.xys00a(date1, date2)[source]¶
For a given TT date, compute the X,Y coordinates of the Celestial Intermediate Pole and the CIO locator s, using the IAU 2000A precession-nutation model.
- Parameters:
- date1double array
- date2double array
- Returns:
- xdouble array
- ydouble array
- sdouble array
Notes
Wraps ERFA function
eraXys00a
. The ERFA documentation is:- - - - - - - - - - e r a X y s 0 0 a - - - - - - - - - - For a given TT date, compute the X,Y coordinates of the Celestial Intermediate Pole and the CIO locator s, using the IAU 2000A precession-nutation model. Given: date1,date2 double TT as a 2-part Julian Date (Note 1) Returned: x,y double Celestial Intermediate Pole (Note 2) s double the CIO locator s (Note 3) Notes: 1) The TT date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=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. 2) The Celestial Intermediate Pole coordinates are the x,y components of the unit vector in the Geocentric Celestial Reference System. 3) The CIO locator s (in radians) positions the Celestial Intermediate Origin on the equator of the CIP. 4) A faster, but slightly less accurate result (about 1 mas for X,Y), can be obtained by using instead the eraXys00b function. Called: eraPnm00a classical NPB matrix, IAU 2000A eraBpn2xy extract CIP X,Y coordinates from NPB matrix eraS00 the CIO locator s, given X,Y, IAU 2000A Reference: McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), IERS Technical Note No. 32, BKG (2004) This revision: 2021 May 11 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.