NAME Time::TAI - International Atomic Time and realisations DESCRIPTION International Atomic Time (TAI) is a time scale produced by an ensemble of atomic clocks around Terra. It attempts to tick at the rate of proper time on the Terran geoid (i.e., at sea level), and thus is the principal realisation of Terrestrial Time (TT). It is the frequency standard underlying Coordinated Universal Time (UTC), and so is indirectly the basis for Terran civil timekeeping. This module represents instants on the TAI time scale as a scalar number of TAI seconds since an epoch. This is an appropriate form for all manner of calculations. The TAI scale is defined with a well-known point at UT2 instant 1958-01-01T00:00:00.0 as calculated by the United States Naval Observatory. That instant is assigned the scalar value zero exactly, making it the epoch for this linear seconds count. This matches the convention used by "Time::TT" for instants on the TT scale. There is also a conventional way to represent TAI instants using day-based notations associated with planetary rotation `time' scales. The `day' of TAI is a nominal period of exactly 86400 TAI seconds, which is slightly shorter than an actual Terran day. The well-known point at UT2 instant 1958-01-01T00:00:00.0 is assigned the label 1958-01-01T00:00:00.0 (MJD 36204.0). Because TAI is not connected to Terran rotation, and so has no inherent concept of a day, it is somewhat misleading to use such day-based notations. Conversion between this notation and the linear count of seconds is supported by this module. This notation does not match the similar day-based notation used for TT. Because TAI is canonically defined only in retrospect, real-time time signals can only approximate it. To achieve microsecond accuracy it is necessary to take account of this process. This module supports conversion of times between different realisations of TAI. INSTALLATION perl Makefile.PL make make test make install AUTHOR Andrew Main (Zefram) COPYRIGHT Copyright (C) 2006, 2007 Andrew Main (Zefram) This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.