sp00¶

erfa.sp00(date1, date2)[source]¶

The TIO locator s’, positioning the Terrestrial Intermediate Origin on the equator of the Celestial Intermediate Pole.

Parameters:

date1double array
date2double array

Returns:

c_retvaldouble array

Notes

Wraps ERFA function eraSp00. The ERFA documentation is:

- - - - - - - -
 e r a S p 0 0
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The TIO locator s', positioning the Terrestrial Intermediate Origin
on the equator of the Celestial Intermediate Pole.

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

Returned (function value):
                double    the TIO 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 TIO locator s' is obtained from polar motion observations by
   numerical integration, and so is in essence unpredictable.
   However, it is dominated by a secular drift of about
   47 microarcseconds per century, which is the approximation
   evaluated by the present function.

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.

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