Py ERFA:docs

- Index
- Modules

### Navigation

- next »
- « previous |
- PyERFA v2.0.0.1 »
- erfa Package »
- pn00

# pn00

erfa.pn00(date1, date2, dpsi, deps)

  Precession-nutation, IAU 2000 model: a multi-purpose function, supporting classical (equinox-based) use directly and CIO-based use indirectly.

  Parameters
    date1 double array
    date2 double array
    dpsi double array
    deps double array
  Returns
    epsa double array
    rb double array
    rp double array
    rbp double array
    rn double array
    rbpn double array

  Notes

  Wraps ERFA function `eraPn00`. The ERFA documentation is:

      - - - - - - - -
       e r a P n 0 0
      - - - - - - - -

      Precession-nutation, IAU 2000 model:  a multi-purpose function,
      supporting classical (equinox-based) use directly and CIO-based
      use indirectly.

      Given:
         date1,date2  double          TT as a 2-part Julian Date (Note 1)
         dpsi,deps    double          nutation (Note 2)

      Returned:
         epsa         double          mean obliquity (Note 3)
         rb           double[3][3]    frame bias matrix (Note 4)
         rp           double[3][3]    precession matrix (Note 5)
         rbp          double[3][3]    bias-precession matrix (Note 6)
         rn           double[3][3]    nutation matrix (Note 7)
         rbpn         double[3][3]    GCRS-to-true matrix (Note 8)

      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 caller is responsible for providing the nutation components;
         they are in longitude and obliquity, in radians and are with
         respect to the equinox and ecliptic of date.  For high-accuracy
         applications, free core nutation should be included as well as
         any other relevant corrections to the position of the CIP.

      3) The returned mean obliquity is consistent with the IAU 2000
         precession-nutation models.

      4) The matrix rb transforms vectors from GCRS to J2000.0 mean
         equator and equinox by applying frame bias.

      5) The matrix rp transforms vectors from J2000.0 mean equator and
         equinox to mean equator and equinox of date by applying
         precession.

      6) The matrix rbp transforms vectors from GCRS to mean equator and
         equinox of date by applying frame bias then precession.  It is
         the product rp x rb.

      7) The matrix rn transforms vectors from mean equator and equinox of
         date to true equator and equinox of date by applying the nutation
         (luni-solar + planetary).

      8) The matrix rbpn transforms vectors from GCRS to true equator and
         equinox of date.  It is the product rn x rbp, applying frame
         bias, precession and nutation in that order.

      9) It is permissible to re-use the same array in the returned
         arguments.  The arrays are filled in the order given.

      Called:
         eraPr00      IAU 2000 precession adjustments
         eraObl80     mean obliquity, IAU 1980
         eraBp00      frame bias and precession matrices, IAU 2000
         eraCr        copy r-matrix
         eraNumat     form nutation matrix
         eraRxr       product of two r-matrices

      Reference:

         Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
         "Expressions for the Celestial Intermediate Pole and Celestial
         Ephemeris Origin consistent with the IAU 2000A precession-
         nutation model", Astron.Astrophys. 400, 1145-1154 (2003)

         n.b. The celestial ephemeris origin (CEO) was renamed "celestial
              intermediate origin" (CIO) by IAU 2006 Resolution 2.

      This revision:  2021 May 11

      Copyright (C) 2013-2021, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.