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# utctai

erfa.utctai(utc1, utc2)

  Time scale transformation: Coordinated Universal Time, UTC, to International Atomic Time, TAI.

  Parameters:
    utc1 double array
    utc2 double array
  Returns:
    tai1 double array
    tai2 double array

  Notes

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

      - - - - - - - - - -
       e r a U t c t a i
      - - - - - - - - - -

      Time scale transformation:  Coordinated Universal Time, UTC, to
      International Atomic Time, TAI.

      Given:
         utc1,utc2  double   UTC as a 2-part quasi Julian Date (Notes 1-4)

      Returned:
         tai1,tai2  double   TAI as a 2-part Julian Date (Note 5)

      Returned (function value):
                    int      status: +1 = dubious year (Note 3)
                                      0 = OK
                                     -1 = unacceptable date

      Notes:

      1) utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any
         convenient way between the two arguments, for example where utc1
         is the Julian Day Number and utc2 is the fraction of a day.

      2) JD cannot unambiguously represent UTC during a leap second unless
         special measures are taken.  The convention in the present
         function is that the JD day represents UTC days whether the
         length is 86399, 86400 or 86401 SI seconds.  In the 1960-1972 era
         there were smaller jumps (in either direction) each time the
         linear UTC(TAI) expression was changed, and these "mini-leaps"
         are also included in the ERFA convention.

      3) The warning status "dubious year" flags UTCs that predate the
         introduction of the time scale or that are too far in the future
         to be trusted.  See eraDat for further details.

      4) The function eraDtf2d converts from calendar date and time of day
         into 2-part Julian Date, and in the case of UTC implements the
         leap-second-ambiguity convention described above.

      5) The returned TAI1,TAI2 are such that their sum is the TAI Julian
         Date.

      Called:
         eraJd2cal    JD to Gregorian calendar
         eraDat       delta(AT) = TAI-UTC
         eraCal2jd    Gregorian calendar to JD

      References:

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

         Explanatory Supplement to the Astronomical Almanac,
         P. Kenneth Seidelmann (ed), University Science Books (1992)

      This revision:  2021 May 11

      Copyright (C) 2013-2023, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.