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<H2><A NAME="SECTION000495000000000000000">SLA_FK54Z - FK5 to FK4, no P.M. or Parallax</A>
<A NAME="xref_SLA_FK54Z"> </A><A NAME="SLA_FK54Z"> </A>
</H2>
<DL>
<DT><STRONG>ACTION:</STRONG>
<DD>Convert a J2000.0 FK5 star position to B1950.0 FK4 assuming
FK5 zero proper motion and parallax.
This routine converts star positions from the new, IAU 1976,
FK5, Fricke system to the old, Bessel-Newcomb, FK4 system.
<P> <DT><STRONG>CALL:</STRONG>
<DD><TT>CALL sla_FK54Z (R2000,D2000,BEPOCH,R1950,D1950,DR1950,DD1950)</TT>
<P> </DL>
<P> <DL>
<DT><STRONG>GIVEN:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>R2000</EM></TD>
<TH ALIGN="LEFT"><B>D</B></TH>
<TD ALIGN="LEFT" NOWRAP>J2000.0 FK5 <IMG WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img24.gif"
ALT="$\alpha$"> (radians)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>D2000</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>J2000.0 FK5 <IMG WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img23.gif"
ALT="$\delta$"> (radians)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>BEPOCH</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>Besselian epoch (<I>e.g.</I> 1950D0)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>RETURNED:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>R1950</EM></TD>
<TH ALIGN="LEFT"><B>D</B></TH>
<TD ALIGN="LEFT" NOWRAP>B1950.0 FK4 <IMG WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img24.gif"
ALT="$\alpha$"> at epoch BEPOCH (radians)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>D1950</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>B1950.0 FK4 <IMG WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img23.gif"
ALT="$\delta$"> at epoch BEPOCH (radians)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DR1950</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>B1950.0 FK4 proper motion in <IMG WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img24.gif"
ALT="$\alpha$">(radians per tropical year)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DD1950</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>B1950.0 FK4 proper motion in <IMG WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img23.gif"
ALT="$\delta$">(radians per tropical year)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>NOTES:</STRONG>
<DD><DL COMPACT>
<DT>1.
<DD>The <IMG WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img24.gif"
ALT="$\alpha$"> proper motions are <IMG WIDTH="13" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img115.gif"
ALT="$\dot{\alpha}$"> rather than
<IMG WIDTH="48" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img116.gif"
ALT="$\dot{\alpha}\cos\delta$">, and are per year rather than per century.
<DT>2.
<DD>Conversion from Julian epoch 2000.0 to Besselian epoch 1950.0
only is provided for. Conversions involving other epochs will
require use of the appropriate precession routines before and
after this routine is called.
<DT>3.
<DD>Unlike in the sla_FK524 routine, the FK5 proper motions, the
parallax and the radial velocity are presumed zero.
<DT>4.
<DD>It was the intention that FK5 should be a close approximation
to an inertial frame, so that distant objects have zero proper
motion; such objects have (in general) non-zero proper motion
in FK4, and this routine returns those <I>fictitious proper
motions</I>.
<DT>5.
<DD>The position returned by this routine is in the B1950
reference frame but at Besselian epoch BEPOCH. For
comparison with catalogues the BEPOCH argument will
frequently be 1950D0.
<DT>6.
<DD>See also sla_FK425, sla_FK45Z, sla_FK524.
</DL></DL>
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<ADDRESS>
<I>SLALIB --- Positional Astronomy Library<BR>Starlink User Note 67<BR>P. T. Wallace<BR>12 October 1999<BR>E-mail:ptw@star.rl.ac.uk</I>
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