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| author | Joseph Hunkeler <jhunkeler@gmail.com> | 2015-03-04 21:21:30 -0500 |
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| committer | Joseph Hunkeler <jhunkeler@gmail.com> | 2015-03-04 21:21:30 -0500 |
| commit | d54fe7c1f704a63824c5bfa0ece65245572e9b27 (patch) | |
| tree | afc52015ffc2c74e0266653eecef1c8ef8ba5d91 /src/slalib/sun67.htx/footnode.html | |
| download | calfuse-d54fe7c1f704a63824c5bfa0ece65245572e9b27.tar.gz | |
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diff --git a/src/slalib/sun67.htx/footnode.html b/src/slalib/sun67.htx/footnode.html new file mode 100644 index 0000000..b6bcb72 --- /dev/null +++ b/src/slalib/sun67.htx/footnode.html @@ -0,0 +1,224 @@ +<!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>Footnotes</TITLE> +<META NAME="description" CONTENT="Footnotes"> +<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="previous" HREF="node228.html"> +<LINK REL="up" HREF="sun67.html"> +</HEAD> +<BODY > +<P><DL> +<DT><A NAME="412">...SLALIB</A> +<DD>The name isn't an acronym; +it just stands for ``Subprogram Library A''. +<PRE>. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +</PRE> +<DT><A NAME="27724">...papers;</A> +<DD>One frame not included in +Figure 1 is that of the Hipparcos catalogue. This is currently the +best available implementation in the optical of the <I>International +Celestial Reference System</I> (ICRS), which is based on extragalactic +radio sources observed by VLBI. The distinction between FK5 J2000 +and Hipparcos coordinates only becomes important when accuracies of +50 mas or better are required. More details are given in +Section 4.14. +<PRE>. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +</PRE> +<DT><A NAME="27833">...<I>equinox</I>.</A> +<DD>With +the introduction of the International Celestial Reference System (ICRS), the +connection between (i) star coordinates and (ii) the Earth's orientation +and orbit has been broken. However, the orientation of the +International Celestial Reference Frame (ICRF) axes was, for convenience, +chosen to match J2000 FK5, and for most practical purposes ICRF coordinates +(for example entries in the Hipparcos catalogue) can be regarded as +synonymous with J2000 FK5. See Section 4.14 for further details. +<PRE>. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +</PRE> +<DT><A NAME="27903">...used.</A> +<DD>An equinox is, however, not required for coordinates +in the International Celestial Reference System. Such coordinates must +be labelled simply ``ICRS'', or the specific catalogue can be mentioned, +such as ``Hipparcos''; constructions such as ``Hipparcos, J2000'' are +redundant and misleading. +<PRE>. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +</PRE> +<DT><A NAME="28038">...catalogues.</A> +<DD>This was +true until the inception of the International Celestial Reference +System, which is based on the idea of axes locked into the +distant background. The coordinates +of the extragalactic sources which realize these +axes have no individual significance; there is a ``no net rotation'' +condition which has to be satisfied each time any revisions take +place. +<PRE>. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +. +</PRE> +</DL><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> |