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<H2><A NAME="SECTION000515000000000000000">
Timescales</A>
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SLALIB provides for conversion between several timescales, and involves
use of one or two others. The full list is as follows:
<UL>
<LI> TAI: International Atomic Time
<LI> UTC: Coordinated Universal Time
<LI> UT: Universal Time
<LI> GMST: Greenwich Mean Sidereal Time
<LI> LAST: Local Apparent Sidereal Time
<LI> TT: Terrestrial Time
<LI> TDB: Barycentric Dynamical Time.
</UL>
Three obsolete timescales should be mentioned here to avoid confusion.
<UL>
<LI> GMT: Greenwich Mean Time - can mean either UTC or UT.
<LI> ET: Ephemeris Time - more or less the same as either TT or TDB.
<LI> TDT: Terrestrial Dynamical Time - former name of TT.
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Atomic Time: TAI</A>
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Universal Time: UTC, UT1</A>
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Sidereal Time: GMST, LAST</A>
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Dynamical Time: TT, TDB</A>
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<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>
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