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diff --git a/src/slalib/sun67.htx/node202.html b/src/slalib/sun67.htx/node202.html new file mode 100644 index 0000000..a161c65 --- /dev/null +++ b/src/slalib/sun67.htx/node202.html @@ -0,0 +1,254 @@ +<!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>Celestial Coordinate Systems</TITLE> +<META NAME="description" CONTENT="Celestial Coordinate Systems"> +<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="node203.html"> +<LINK REL="previous" HREF="node200.html"> +<LINK REL="up" HREF="node197.html"> +<LINK REL="next" HREF="node203.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html2472" HREF="node203.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2470" HREF="node197.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2464" HREF="node201.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="tex2html2473" HREF="node203.html">Precession and Nutation</A> +<BR> +<B>Up:</B> <A NAME="tex2html2471" HREF="node197.html">EXPLANATION AND EXAMPLES</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2465" HREF="node201.html">Using vectors</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H2><A NAME="SECTION00053000000000000000"> +Celestial Coordinate Systems</A> +</H2> +SLALIB has routines to perform transformations +of celestial positions between different spherical +coordinate systems, including those shown in the following table: +<P> +<DIV ALIGN="CENTER"> +<TABLE CELLPADDING=3 BORDER="1"> +<TR VALIGN="TOP"><TH ALIGN="LEFT" NOWRAP><I>system</I></TH> +<TH ALIGN="CENTER" NOWRAP><I>symbols</I></TH> +<TH ALIGN="CENTER" NOWRAP><I>longitude</I></TH> +<TH ALIGN="CENTER" NOWRAP><I>latitude</I></TH> +<TH ALIGN="CENTER" NOWRAP><I>x-y plane</I></TH> +<TH ALIGN="CENTER" NOWRAP><I>long. zero</I></TH> +<TH ALIGN="CENTER" NOWRAP><I>RH/LH</I></TH> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT" NOWRAP>horizon</TD> +<TD ALIGN="CENTER" NOWRAP>-</TD> +<TD ALIGN="CENTER" NOWRAP>azimuth</TD> +<TD ALIGN="CENTER" NOWRAP>elevation</TD> +<TD ALIGN="CENTER" NOWRAP>horizontal</TD> +<TD ALIGN="CENTER" NOWRAP>north</TD> +<TD ALIGN="CENTER" NOWRAP>L</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT" NOWRAP>equatorial</TD> +<TD ALIGN="CENTER" NOWRAP><IMG WIDTH="28" HEIGHT="27" ALIGN="MIDDLE" BORDER="0" + SRC="img91.gif" + ALT="$\alpha,\delta$"></TD> +<TD ALIGN="CENTER" NOWRAP>R.A.</TD> +<TD ALIGN="CENTER" NOWRAP>Dec.</TD> +<TD ALIGN="CENTER" NOWRAP>equator</TD> +<TD ALIGN="CENTER" NOWRAP>equinox</TD> +<TD ALIGN="CENTER" NOWRAP>R</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT" NOWRAP>local equ.</TD> +<TD ALIGN="CENTER" NOWRAP><IMG WIDTH="27" HEIGHT="27" ALIGN="MIDDLE" BORDER="0" + SRC="img65.gif" + ALT="$h,\delta$"></TD> +<TD ALIGN="CENTER" NOWRAP>H.A.</TD> +<TD ALIGN="CENTER" NOWRAP>Dec.</TD> +<TD ALIGN="CENTER" NOWRAP>equator</TD> +<TD ALIGN="CENTER" NOWRAP>meridian</TD> +<TD ALIGN="CENTER" NOWRAP>L</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT" NOWRAP>ecliptic</TD> +<TD ALIGN="CENTER" NOWRAP><IMG WIDTH="29" HEIGHT="27" ALIGN="MIDDLE" BORDER="0" + SRC="img253.gif" + ALT="$\lambda,\beta$"></TD> +<TD ALIGN="CENTER" NOWRAP>ecl. long.</TD> +<TD ALIGN="CENTER" NOWRAP>ecl. lat.</TD> +<TD ALIGN="CENTER" NOWRAP>ecliptic</TD> +<TD ALIGN="CENTER" NOWRAP>equinox</TD> +<TD ALIGN="CENTER" NOWRAP>R</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT" NOWRAP>galactic</TD> +<TD ALIGN="CENTER" NOWRAP><IMG WIDTH="45" HEIGHT="32" ALIGN="MIDDLE" BORDER="0" + SRC="img254.gif" + ALT="$l^{I\!I},b^{I\!I}$"></TD> +<TD ALIGN="CENTER" NOWRAP>gal. long.</TD> +<TD ALIGN="CENTER" NOWRAP>gal. lat.</TD> +<TD ALIGN="CENTER" NOWRAP>gal. equator</TD> +<TD ALIGN="CENTER" NOWRAP>gal. centre</TD> +<TD ALIGN="CENTER" NOWRAP>R</TD> +</TR> +<TR VALIGN="TOP"><TD ALIGN="LEFT" NOWRAP>supergalactic</TD> +<TD ALIGN="CENTER" NOWRAP>SGL,SGB</TD> +<TD ALIGN="CENTER" NOWRAP>SG long.</TD> +<TD ALIGN="CENTER" NOWRAP>SG lat.</TD> +<TD ALIGN="CENTER" NOWRAP>SG equator</TD> +<TD ALIGN="CENTER" NOWRAP>node w. gal. equ.</TD> +<TD ALIGN="CENTER" NOWRAP>R</TD> +</TR> +</TABLE></DIV> +Transformations between <IMG WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img29.gif" + ALT="$[\,h,\delta\,]$"> and <IMG WIDTH="66" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img28.gif" + ALT="$[\,Az,El~]$"> can be performed by +calling +sla_E2H +and +sla_H2E, +or, in double precision, +sla_DE2H +and +sla_DH2E. +There is also a routine for obtaining +zenith distance alone for a given <IMG WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img29.gif" + ALT="$[\,h,\delta\,]$">,sla_ZD, +and one for determining the parallactic angle, +sla_PA. +Three routines are included which relate to altazimuth telescope +mountings. For a given <IMG WIDTH="41" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img29.gif" + ALT="$[\,h,\delta\,]$"> and latitude, +sla_ALTAZ +returns the azimuth, elevation and parallactic angle, plus +velocities and accelerations for sidereal tracking. +The routines +sla_PDA2H +and +sla_PDQ2H +predict at what hour angle a given azimuth or +parallactic angle will be reached. +<P> +The routines +sla_EQECL +and +sla_ECLEQ +transform between ecliptic +coordinates and <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$">; there is also a routine for generating the +equatorial to ecliptic rotation matrix for a given date: +sla_ECMAT. +<P> +For conversion between Galactic coordinates and <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> there are +two sets of routines, depending on whether the <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> is +old-style, B1950, or new-style, J2000; +sla_EG50 +and +sla_GE50 +are <IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> to <IMG WIDTH="59" HEIGHT="32" ALIGN="MIDDLE" BORDER="0" + SRC="img98.gif" + ALT="$[\,l^{I\!I},b^{I\!I}\,]$"> and <I>vice versa</I> for the B1950 case, while +sla_EQGAL +and +sla_GALEQ +are the J2000 equivalents. +<P> +Finally, the routines +sla_GALSUP +and +sla_SUPGAL +transform <IMG WIDTH="59" HEIGHT="32" ALIGN="MIDDLE" BORDER="0" + SRC="img98.gif" + ALT="$[\,l^{I\!I},b^{I\!I}\,]$"> to de Vaucouleurs supergalactic longitude and latitude +and <I>vice versa.</I> +<P> +It should be appreciated that the table, above, constitutes +a gross oversimplification. Apparently +simple concepts such as equator, equinox <I>etc.</I> are apt to be very hard to +pin down precisely (polar motion, orbital perturbations ...) and +some have several interpretations, all subtly different. The various +frames move in complicated ways with respect to one another or to +the stars (themselves in motion). And in some instances the +coordinate system is slightly distorted, so that the +ordinary rules of spherical trigonometry no longer strictly apply. +<P> +These <I>caveats</I> +apply particularly to the bewildering variety of different +<IMG WIDTH="42" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img3.gif" + ALT="$[\,\alpha,\delta\,]$"> systems that are in use. Figure 1 shows how +some of these systems are related, to one another and +to the direction in which a celestial source actually +appears in the sky. At the top of the diagram are +the various sorts of <I>mean place</I> +found in star catalogues and papers;<A NAME="tex2html3" HREF="footnode.html#27724"><SUP><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]" SRC="foot_motif.gif"></SUP></A> at the bottom is the +<I>observed</I> <IMG WIDTH="66" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" + SRC="img28.gif" + ALT="$[\,Az,El~]$">, where a perfect theodolite would +be pointed to see the source; and in the body of +the diagram are +the intermediate processing steps and coordinate +systems. To help +understand this diagram, and the SLALIB routines that can +be used to carry out the various calculations, we will look at the coordinate +systems involved, and the astronomical phenomena that +affect them. +<P> +<BR> +<DIV ALIGN="CENTER"><A NAME="27722"> </A> +<TABLE> +<CAPTION><STRONG>Figure 1:</STRONG> +Relationship Between Celestial Coordinates</CAPTION> +<TR><TD><IMG WIDTH="450" HEIGHT="642" + SRC="img255.gif" + ALT="\begin{figure} +\begin{center} +\begin{tabular} +{\vert cccccc\vert} \hline +& & & &... + ...2000, all of the precession and E-terms corrections +are superfluous.\end{figure}"></TD></TR> +</TABLE> +</DIV> +<BR> +<BR> <HR> +<A NAME="tex2html2472" HREF="node203.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2470" HREF="node197.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2464" HREF="node201.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="tex2html2473" HREF="node203.html">Precession and Nutation</A> +<BR> +<B>Up:</B> <A NAME="tex2html2471" HREF="node197.html">EXPLANATION AND EXAMPLES</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2465" HREF="node201.html">Using vectors</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> |