era.pnm06a.md

eraPnm06a

rbpn = ERFA.pnm06a(date1, date2)

Form the matrix of precession-nutation for a given date (including frame bias), equinox based, IAU 2006 precession and IAU 2000A nutation models.

Given:

   date1,date2 double       TT as a 2-part Julian Date (Note 1)

Returned:

   rbpn        double[3][3] bias-precession-nutation matrix (Note 2)

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) = rbpn * V(GCRS), where the p-vector V(date) is with respect to the true equatorial triad of date date1+date2 and the p-vector V(GCRS) is with respect to the Geocentric Celestial Reference System (IAU, 2000).

Called:

   eraPfw06     bias-precession F-W angles, IAU 2006
   eraNut06a    nutation, IAU 2006/2000A
   eraFw2m      F-W angles to r-matrix

Reference:

Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855.

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.