pmat76¶
- erfa.pmat76(date1, date2)[source]¶
Precession matrix from J2000.0 to a specified date, IAU 1976 model.
- Parameters:
- date1double array
- date2double array
- Returns:
- rmatpdouble array
Notes
Wraps ERFA function
eraPmat76
. The ERFA documentation is:- - - - - - - - - - e r a P m a t 7 6 - - - - - - - - - - Precession matrix from J2000.0 to a specified date, IAU 1976 model. Given: date1,date2 double ending date, TT (Note 1) Returned: rmatp double[3][3] precession matrix, J2000.0 -> date1+date2 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 matrix operates in the sense V(date) = RMATP * V(J2000), where the p-vector V(J2000) is with respect to the mean equatorial triad of epoch J2000.0 and the p-vector V(date) is with respect to the mean equatorial triad of the given date. 3) Though the matrix method itself is rigorous, the precession angles are expressed through canonical polynomials which are valid only for a limited time span. In addition, the IAU 1976 precession rate is known to be imperfect. The absolute accuracy of the present formulation is better than 0.1 arcsec from 1960AD to 2040AD, better than 1 arcsec from 1640AD to 2360AD, and remains below 3 arcsec for the whole of the period 500BC to 3000AD. The errors exceed 10 arcsec outside the range 1200BC to 3900AD, exceed 100 arcsec outside 4200BC to 5600AD and exceed 1000 arcsec outside 6800BC to 8200AD. Called: eraPrec76 accumulated precession angles, IAU 1976 eraIr initialize r-matrix to identity eraRz rotate around Z-axis eraRy rotate around Y-axis eraCr copy r-matrix References: Lieske, J.H., 1979, Astron.Astrophys. 73, 282. equations (6) & (7), p283. Kaplan,G.H., 1981. USNO circular no. 163, pA2. This revision: 2021 May 11 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.