From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node218.html | 91 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 91 insertions(+) create mode 100644 src/slalib/sun67.htx/node218.html (limited to 'src/slalib/sun67.htx/node218.html') 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 @@ + + + + +Atomic Time: TAI + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: Universal Time: UTC, UT1 +
+Up: Timescales +
+ Previous: Timescales +

+

+

+Atomic Time: TAI +

+International Atomic Time 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. +

+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. +

+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 ftp://maia.usno.navy.mil/ser7/tai-utc.dat. +

+

+ +next + +up + +previous +
+ Next: Universal Time: UTC, UT1 +
+Up: Timescales +
+ Previous: Timescales +

+

+

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +
+ + -- cgit