erfa.utctai(utc1, utc2)[source]

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

utc1double array
utc2double array
tai1double array
tai2double array


Wraps ERFA function eraUtctai. The ERFA documentation is:

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 e r a U t c t a i
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Time scale transformation:  Coordinated Universal Time, UTC, to
International Atomic Time, TAI.

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

   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


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

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


   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.