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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/node73.html | |
| download | calfuse-d54fe7c1f704a63824c5bfa0ece65245572e9b27.tar.gz | |
Initial commit
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| -rw-r--r-- | src/slalib/sun67.htx/node73.html | 131 |
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diff --git a/src/slalib/sun67.htx/node73.html b/src/slalib/sun67.htx/node73.html new file mode 100644 index 0000000..fca730c --- /dev/null +++ b/src/slalib/sun67.htx/node73.html @@ -0,0 +1,131 @@ +<!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>SLA_DT - Approximate ET minus UT</TITLE> +<META NAME="description" CONTENT="SLA_DT - Approximate ET minus UT"> +<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="node74.html"> +<LINK REL="previous" HREF="node72.html"> +<LINK REL="up" HREF="node13.html"> +<LINK REL="next" HREF="node74.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html1156" HREF="node74.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html1154" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html1148" HREF="node72.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="tex2html1157" HREF="node74.html">SLA_DTF2D - Hour,Min,Sec to Days</A> +<BR> +<B>Up:</B> <A NAME="tex2html1155" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html1149" HREF="node72.html">SLA_DSEP - Angle Between 2 Points on Sphere</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H2><A NAME="SECTION000460000000000000000">SLA_DT - Approximate ET minus UT</A> +<A NAME="xref_SLA_DT"> </A><A NAME="SLA_DT"> </A> +</H2> + <DL> +<DT><STRONG>ACTION:</STRONG> +<DD>Estimate <IMG WIDTH="16" HEIGHT="13" ALIGN="BOTTOM" BORDER="0" + SRC="img19.gif" + ALT="$\Delta$">T, the offset between dynamical time +and Universal Time, for a given historical epoch. +<P> <DT><STRONG>CALL:</STRONG> +<DD><TT>D = sla_DT (EPOCH)</TT> +<P> </DL> +<P> <DL> +<DT><STRONG>GIVEN:</STRONG> +<DD> +<BR> +<TABLE CELLPADDING=3> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>EPOCH</EM></TD> +<TH ALIGN="LEFT"><B>D</B></TH> +<TH ALIGN="LEFT" NOWRAP>(Julian) epoch (<I>e.g.</I> 1850D0)</TH> +</TR> +</TABLE></DL> +<P> <DL> +<DT><STRONG>RETURNED:</STRONG> +<DD> +<BR> +<TABLE CELLPADDING=3> +<TR VALIGN="TOP"><TD ALIGN="LEFT"><EM>sla_DT</EM></TD> +<TH ALIGN="LEFT"><B>D</B></TH> +<TD ALIGN="LEFT" NOWRAP>approximate ET-UT (after 1984, TT-UT1) in seconds</TD> +</TR> +</TABLE></DL> +<P> <DL> +<DT><STRONG>NOTES:</STRONG> +<DD><DL COMPACT> +<DT>1. +<DD>Depending on the epoch, one of three parabolic approximations +is used: +<PRE><TT> +before AD 979 Stephenson & Morrison's 390 BC to AD 948 model + AD 979 to AD 1708 Stephenson & Morrison's AD 948 to AD 1600 model + after AD 1708 McCarthy & Babcock's post-1650 model +</TT></PRE> + The breakpoints are chosen to ensure continuity: they occur + at places where the adjacent models give the same answer as + each other. + <DT>2. +<DD>The accuracy is modest, with errors of up to <IMG WIDTH="24" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img86.gif" + ALT="$20^{\rm s}$"> during + the interval since 1650, rising to perhaps <IMG WIDTH="30" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img87.gif" + ALT="$30^{\rm m}$"> by 1000 BC. Comparatively accurate values from AD 1600 + are tabulated in + the <I>Astronomical Almanac</I> (see section K8 of the 1995 + edition). + <DT>3. +<DD>The use of <TT>DOUBLE PRECISION</TT> for both argument and result is + simply for compatibility with other SLALIB time routines. + <DT>4. +<DD>The models used are based on a lunar tidal acceleration value + of + <IMG WIDTH="52" HEIGHT="35" ALIGN="MIDDLE" BORDER="0" + SRC="img88.gif" + ALT="$-26\hspace{-0.05em}^{'\hspace{-0.1em}'}\hspace{-0.4em}.00$"> per century. + </DL></DL> +<P> <DL> +<DT><STRONG>REFERENCE:</STRONG> +<DD>Seidelmann, P.K. (ed), 1992. <I>Explanatory +Supplement to the Astronomical Almanac,</I> ISBN 0-935702-68-7. + This contains references to the papers by Stephenson & Morrison + and by McCarthy & Babcock which describe the models used here. + </DL> +<BR> <HR> +<A NAME="tex2html1156" HREF="node74.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html1154" HREF="node13.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html1148" HREF="node72.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="tex2html1157" HREF="node74.html">SLA_DTF2D - Hour,Min,Sec to Days</A> +<BR> +<B>Up:</B> <A NAME="tex2html1155" HREF="node13.html">SUBPROGRAM SPECIFICATIONS</A> +<BR> +<B> Previous:</B> <A NAME="tex2html1149" HREF="node72.html">SLA_DSEP - Angle Between 2 Points on Sphere</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> |