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- Estimate the offset between dynamical time and UT
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<H2><A NAME="SECTION000319000000000000000"></A><A NAME="____palDt_"></A>
<BR>
palDt

   palDt
-   Estimate the offset between dynamical time and UT

</H2>
      <DL>
<DT><STRONG>Description:</STRONG></DT>
<DD><DL>
<DD>Estimate the offset between dynamical time and Universal Time
      for a given historical epoch.

</DD>
</DL>
      
<BR>   
   
</DD>
<DT><STRONG>Invocation:</STRONG></DT>
<DD><DL>
<DD><TT>      double palDt( double epoch );
   </TT>
      
</DD>
</DL>
      
<BR>

</DD>
<DT><STRONG>Arguments:</STRONG></DT>
<DD>
<BR>      <DL>
<DT><STRONG>
         epoch = double (Given)
      </STRONG></DT>
<DD>
         Julian epoch (e.g. 1850.0)
      

</DD>
</DL>
      
<BR>

</DD>
<DT><STRONG>Returned Value:</STRONG></DT>
<DD>
<BR>      <DL>
<DT><STRONG>
         palDt = double
      </STRONG></DT>
<DD>
         Rough estimate of ET-UT (after 1984, TT-UT) at the
         given epoch, in seconds.
      

</DD>
</DL>
      
<BR>   
   
</DD>
<DT><STRONG>Notes:</STRONG></DT>
<DD><UL>
<LI>Depending on the epoch, one of three parabolic approximations
           is used:

<P>
</LI>
</UL>
      
<BR>
before 979    Stephenson &amp; Morrison<TT>'</TT>s 390 BC to AD 948 model
          979 to 1708   Stephenson &amp; Morrison<TT>'</TT>s 948 to 1600 model
          after 1708    McCarthy &amp; Babcock<TT>'</TT>s post-1650 model

<P>
The breakpoints are chosen to ensure continuity:  they occur
        at places where the adjacent models give the same answer as
        each other.

<UL>
<LI>The accuracy is modest, with errors of up to 20 sec during
           the interval since 1650, rising to perhaps 30 min by 1000 BC.
           Comparatively accurate values from AD 1600 are tabulated in
           the Astronomical Almanac (see section K8 of the 1995 AA).

<P>
</LI>
<LI>The use of double-precision for both argument and result is
           purely for compatibility with other SLALIB time routines.

<P>
</LI>
<LI>The models used are based on a lunar tidal acceleration value
           of -26.00 arcsec per century.

</LI>
</UL>
      
<BR>

</DD>
<DT><STRONG>
      See Also
   </STRONG></DT>
<DD>Explanatory Supplement to the Astronomical Almanac,
      ed P.K.Seidelmann, University Science Books (1992),
      section 2.553, p83.  This contains references to
      the Stephenson &amp; Morrison and McCarthy &amp; Babcock
      papers.

</DD>
</DL>
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