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diff --git a/src/slalib/sun67.htx/node218.html b/src/slalib/sun67.htx/node218.html new file mode 100644 index 0000000..106412e --- /dev/null +++ b/src/slalib/sun67.htx/node218.html @@ -0,0 +1,91 @@ +<!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>Atomic Time: TAI</TITLE> +<META NAME="description" CONTENT="Atomic Time: TAI"> +<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="node219.html"> +<LINK REL="previous" HREF="node217.html"> +<LINK REL="up" HREF="node217.html"> +<LINK REL="next" HREF="node219.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html2635" HREF="node219.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2633" HREF="node217.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2627" HREF="node217.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="tex2html2636" HREF="node219.html">Universal Time: UTC, UT1</A> +<BR> +<B>Up:</B> <A NAME="tex2html2634" HREF="node217.html">Timescales</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2628" HREF="node217.html">Timescales</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H3><A NAME="SECTION000515100000000000000"> +Atomic Time: TAI</A> +</H3> +<I>International Atomic Time</I> TAI is a laboratory timescale. Its +unit is the SI second, which is defined in terms of a +defined number +of wavelengths of the radiation produced by a certain electronic +transition in the caesium 133 atom. It +is realized through a changing +population of high-precision atomic clocks held +at standards institutes in various countries. There is an +elaborate process of continuous intercomparison, leading to +a weighted average of all the clocks involved. +<P> +Though TAI shares the same second as the more familiar UTC, the +two timescales are noticeably separated in epoch because of the +build-up of leap seconds. At the time of writing, UTC +lags about half a minute behind TAI. +<P> +For any given date, the difference TAI-UTC +can be obtained by calling the SLALIB routine +sla_DAT. +Note, however, that an up-to-date copy of the routine must be used if +the most recent leap seconds are required. For applications +where this is critical, mechanisms independent of SLALIB +and under local control must +be set up; in such cases +sla_DAT +can be useful as an +independent check, for test dates within the range of the +available version. Up-to-date information on TAI-UTC is available +from <TT>ftp://maia.usno.navy.mil/ser7/tai-utc.dat</TT>. +<P> +<BR> <HR> +<A NAME="tex2html2635" HREF="node219.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2633" HREF="node217.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2627" HREF="node217.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="tex2html2636" HREF="node219.html">Universal Time: UTC, UT1</A> +<BR> +<B>Up:</B> <A NAME="tex2html2634" HREF="node217.html">Timescales</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2628" HREF="node217.html">Timescales</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> |