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<H2><A NAME="SECTION0004113000000000000000">SLA_MAP - Mean to Apparent</A>
<A NAME="xref_SLA_MAP"> </A><A NAME="SLA_MAP"> </A>
</H2>
<DL>
<DT><STRONG>ACTION:</STRONG>
<DD>Transform star <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img3.gif"
ALT="$[\,\alpha,\delta\,]$"> from mean place to geocentric apparent.
The reference frames and timescales used are post IAU 1976.
<P> <DT><STRONG>CALL:</STRONG>
<DD><TT>CALL sla_MAP (RM, DM, PR, PD, PX, RV, EQ, DATE, RA, DA)</TT>
<P> </DL>
<P> <DL>
<DT><STRONG>GIVEN:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RM,DM</EM></TD>
<TH ALIGN="LEFT"><B>D</B></TH>
<TD ALIGN="LEFT" NOWRAP>mean <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img3.gif"
ALT="$[\,\alpha,\delta\,]$"> (radians)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>PR,PD</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>proper motions: <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img3.gif"
ALT="$[\,\alpha,\delta\,]$"> changes per Julian year</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>PX</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>parallax (arcsec)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RV</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>radial velocity (km s<SUP>-1</SUP>, +ve if receding)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>EQ</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>epoch and equinox of star data (Julian)</TD>
</TR>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DATE</EM></TD>
<TD ALIGN="LEFT"><B>D</B></TD>
<TD ALIGN="LEFT" NOWRAP>TDB for apparent place (JD-2400000.5)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>RETURNED:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>RA,DA</EM></TD>
<TH ALIGN="LEFT"><B>D</B></TH>
<TD ALIGN="LEFT" NOWRAP>apparent <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img3.gif"
ALT="$[\,\alpha,\delta\,]$"> (radians)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>NOTES:</STRONG>
<DD><DL COMPACT>
<DT>1.
<DD>EQ is the Julian epoch specifying both the reference
frame and the epoch of the position - usually 2000.
For positions where the epoch and equinox are
different, use the routine sla_PM to apply proper
motion corrections before using this routine.
<DT>2.
<DD>The distinction between the required TDB and TT is
always negligible. Moreover, for all but the most
critical applications UTC is adequate.
<DT>3.
<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>4.
<DD>This routine may be wasteful for some applications
because it recomputes the Earth position/velocity and
the precession/nutation matrix each time, and because
it allows for parallax and proper motion. Where
multiple transformations are to be carried out for one
epoch, a faster method is to call the sla_MAPPA routine
once and then either the sla_MAPQK routine (which includes
parallax and proper motion) or sla_MAPQKZ (which assumes
zero parallax and FK5 proper motion).
</DL></DL>
<P> <DL>
<DT><STRONG>REFERENCES:</STRONG>
<DD><DL COMPACT>
<DT>1.
<DD>1984 <I>Astronomical Almanac</I>, pp B39-B41.
<DT>2.
<DD>Lederle & Schwan, 1984. <I>Astr.Astrophys.</I> <B>134</B>, 1-6.
</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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