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diff --git a/src/slalib/sun67.htx/node208.html b/src/slalib/sun67.htx/node208.html new file mode 100644 index 0000000..cc2b337 --- /dev/null +++ b/src/slalib/sun67.htx/node208.html @@ -0,0 +1,92 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<!--Converted with LaTeX2HTML 97.1 (release) (July 13th, 1997) + by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds +* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan +* with significant contributions from: + Jens Lippman, Marek Rouchal, Martin Wilck and others --> +<HTML> +<HEAD> +<TITLE>Parallax and Radial Velocity</TITLE> +<META NAME="description" CONTENT="Parallax and Radial Velocity"> +<META NAME="keywords" CONTENT="sun67"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso_8859_1"> +<LINK REL="STYLESHEET" HREF="sun67.css"> +<LINK REL="next" HREF="node209.html"> +<LINK REL="previous" HREF="node207.html"> +<LINK REL="up" HREF="node197.html"> +<LINK REL="next" HREF="node209.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html2531" HREF="node209.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2529" HREF="node197.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2523" HREF="node207.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html2532" HREF="node209.html">Aberration</A> +<BR> +<B>Up:</B> <A NAME="tex2html2530" HREF="node197.html">EXPLANATION AND EXAMPLES</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2524" HREF="node207.html">Proper Motion</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H2><A NAME="SECTION00058000000000000000"> +Parallax and Radial Velocity</A> +</H2> +For the utmost accuracy and the nearest stars, allowance can +be made for <I>annual parallax</I> and for the effects of perspective +on the proper motion. +<P> +Parallax is appreciable only for nearby stars; even +the nearest, Proxima Centauri, is displaced from its average +position by less than +an arcsecond as the Earth revolves in its orbit. +<P> +For stars with a known parallax, knowledge of the radial velocity +allows the proper motion to be expressed as an actual space +motion in 3 dimensions. The proper motion is, +in fact, a snapshot of the transverse component of the +space motion, and in the case of nearby stars will +change with time due to perspective. +<P> +SLALIB does not provide facilities for handling parallax +and radial-velocity on their own, but their contribution is +allowed for in such routines as +sla_PM, +sla_MAP +and +sla_FK425. +Catalogue mean +places do not include the effects of parallax and are therefore +<I>barycentric</I>; when pointing telescopes <I>etc.</I> it is +usually most efficient to apply the slowly-changing +parallax correction to the mean place of the target early on +and to work with the <I>geocentric</I> mean place. This latter +approach is implied in Figure 1. +<P> +<BR> <HR> +<A NAME="tex2html2531" HREF="node209.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2529" HREF="node197.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2523" HREF="node207.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html2532" HREF="node209.html">Aberration</A> +<BR> +<B>Up:</B> <A NAME="tex2html2530" HREF="node197.html">EXPLANATION AND EXAMPLES</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2524" HREF="node207.html">Proper Motion</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<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> +</ADDRESS> +</BODY> +</HTML> |