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<H2><A NAME="SECTION000449000000000000000">SLA_DMOON - Approx Moon Pos/Vel</A>
<A NAME="xref_SLA_DMOON"> </A><A NAME="SLA_DMOON"> </A>
</H2>
<DL>
<DT><STRONG>ACTION:</STRONG>
<DD>Approximate geocentric position and velocity of the Moon
(double precision).
<P> <DT><STRONG>CALL:</STRONG>
<DD><TT>CALL sla_DMOON (DATE, PV)</TT>
<P> </DL>
<P> <DL>
<DT><STRONG>GIVEN:</STRONG>
<DD>
<BR>
<TABLE CELLPADDING=3>
<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>DATE</EM></TD>
<TH ALIGN="LEFT"><B>D</B></TH>
<TD ALIGN="LEFT" NOWRAP>TDB (loosely ET) as a Modified Julian Date (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>PV</EM></TD>
<TH ALIGN="LEFT"><B>D(6)</B></TH>
<TD ALIGN="LEFT" NOWRAP>Moon <IMG WIDTH="106" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img51.gif"
ALT="$[\,x,y,z,\dot{x},\dot{y},\dot{z}\,]$">, mean equator and equinox
of date (AU, AU s<SUP>-1</SUP>)</TD>
</TR>
</TABLE></DL>
<P> <DL>
<DT><STRONG>NOTES:</STRONG>
<DD><DL COMPACT>
<DT>1.
<DD>This routine is a full implementation of the algorithm
published by Meeus (see reference).
<DT>2.
<DD>Meeus quotes accuracies of <IMG WIDTH="25" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img74.gif"
ALT="$10\hspace{-0.05em}^{'\hspace{-0.1em}'}$"> in longitude,
<IMG WIDTH="17" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img75.gif"
ALT="$3\hspace{-0.05em}^{'\hspace{-0.1em}'}$"> in latitude and
<IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img76.gif"
ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.2$"> arcsec in HP
(equivalent to about 20 km in distance). Comparison with
JPL DE200 over the interval 1960-2025 gives RMS errors of
<P> <IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img77.gif"
ALT="$3\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.7$"> and 83 mas/hour in longitude,
<P> <IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img78.gif"
ALT="$2\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.3$"> arcsec and 48 mas/hour in latitude,
11 km and 81 mm/s in distance.
The maximum errors over the same interval are
<IMG WIDTH="25" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img79.gif"
ALT="$18\hspace{-0.05em}^{'\hspace{-0.1em}'}$"> and
<IMG WIDTH="31" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img80.gif"
ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.50$"> /hour in longitude,
<IMG WIDTH="25" HEIGHT="17" ALIGN="BOTTOM" BORDER="0"
SRC="img43.gif"
ALT="$11\hspace{-0.05em}^{'\hspace{-0.1em}'}$"> and
<IMG WIDTH="31" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img81.gif"
ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.24$"> /hour in latitude,
40 km and 0.29 m/s in distance.
<DT>3.
<DD>The original algorithm is expressed in terms of the obsolete
timescale <I>Ephemeris Time</I>. Either TDB or TT can be used,
but not UT without incurring significant errors (<IMG WIDTH="25" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img82.gif"
ALT="$30\hspace{-0.05em}^{'\hspace{-0.1em}'}$"> at
the present time) due to the Moon's
<IMG WIDTH="23" HEIGHT="18" ALIGN="BOTTOM" BORDER="0"
SRC="img83.gif"
ALT="$0\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.5$"> /s movement.
<DT>4.
<DD>The algorithm is based on pre IAU 1976 standards. However,
the result has been moved onto the new (FK5) equinox, an
adjustment which is in any case much smaller than the
intrinsic accuracy of the procedure.
<DT>5.
<DD>Velocity is obtained by a complete analytical differentiation
of the Meeus model.
</DL></DL>
<P> <DL>
<DT><STRONG>REFERENCE:</STRONG>
<DD>Meeus, <I>l'Astronomie</I>, June 1984, p348.
</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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