Py ERFA:docs

- Index
- Modules

### Navigation

- next »
- « previous |
- PyERFA v2.0.0.1 »
- erfa Package »
- s00

# s00

erfa.s00(date1, date2, x, y)

  The CIO locator s, positioning the Celestial Intermediate Origin on the equator of the Celestial Intermediate Pole, given the CIP’s X,Y coordinates.

  Parameters
    date1 double array
    date2 double array
    x double array
    y double array
  Returns
    c_retval double array

  Notes

  Wraps ERFA function `eraS00`. The ERFA documentation is:

      - - - - - - -
       e r a S 0 0
      - - - - - - -

      The CIO locator s, positioning the Celestial Intermediate Origin on
      the equator of the Celestial Intermediate Pole, given the CIP's X,Y
      coordinates.  Compatible with IAU 2000A precession-nutation.

      Given:
         date1,date2   double    TT as a 2-part Julian Date (Note 1)
         x,y           double    CIP coordinates (Note 3)

      Returned (function value):
                       double    the CIO locator s in radians (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 CIO locator s is the difference between the right ascensions
         of the same point in two systems:  the two systems are the GCRS
         and the CIP,CIO, and the point is the ascending node of the
         CIP equator.  The quantity s remains below 0.1 arcsecond
         throughout 1900-2100.

      3) The series used to compute s is in fact for s+XY/2, where X and Y
         are the x and y components of the CIP unit vector;  this series
         is more compact than a direct series for s would be.  This
         function requires X,Y to be supplied by the caller, who is
         responsible for providing values that are consistent with the
         supplied date.

      4) The model is consistent with the IAU 2000A precession-nutation.

      Called:
         eraFal03     mean anomaly of the Moon
         eraFalp03    mean anomaly of the Sun
         eraFaf03     mean argument of the latitude of the Moon
         eraFad03     mean elongation of the Moon from the Sun
         eraFaom03    mean longitude of the Moon's ascending node
         eraFave03    mean longitude of Venus
         eraFae03     mean longitude of Earth
         eraFapa03    general accumulated precession in longitude

      References:

         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.

         McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
         IERS Technical Note No. 32, BKG (2004)

      This revision:  2021 May 11

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