Leap Second Table
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The Leap Second Table (UTCTAI.dat file) is an editable ASCII text file that contains historical and predicted occurrences of leap seconds. It is based on historical data provided by The US Naval Observatory and predicted data provided by Goddard Space Flight Center.
FreeFlyer will add 9 seconds to any date before the first epoch or row in the table (11317.5 - Jan 1, 1972), and then will add a single leap second based on the epoch that is in the first column of the UTCTAI.dat file.
Predicted and definitive leap second occurrences can be found on the USNO web site: http://maia.usno.navy.mil/. Since the Leap Second Table is an ASCII text file, it can easily be edited by simply adding the time of the leap second (in UTC Julian (GSFC)) and a comment (for user benefit).
The format of the file is shown below.