[ntp:questions] Leap second functional question

Unruh unruh-spam at physics.ubc.ca
Tue Feb 19 21:21:56 UTC 2008

Nero Imhard <nim at pipe.nl> writes:

>Unruh wrote:

>> No, in UTC all years are 86400 seconds, even if during that year a 
>> second was added or subtracted.

>Well, apart from the fact that a day is not a year, there is no denying
>that between 0:00 UTC on one day and the next, there have elapsed 86401
>SI seconds if there has been a leap second.

Yes, but UTC ignores that and assumes that only 86400 seconds have occured,
even though 86401 actually occured. It simply ignores that extra second.
That is the beauty of utc.

>> year with a leap second added has 86400 UTC seconds but 86401 TAI 
>> seconds.

>Both UTC and TAI count SI-seconds, but you seem to differentiate between
>the two. How you want to express durations "in UTC" or "in TAI" is
>unclear to me and I prefer avoid it altogether.

Yes, I differentiate because UTC does. UTC assumes despite the facts that
only 86400 seconds have occured. You may have lived through and experienced
that extra second ( eg having to wait and extra second before you yelled
Happy New Year) but UTC erases it from history. It says that that Dec only had 
31*86400 seconds, no matter what your experience said.

 Thus the number of seconds from Dec 1 0:0:0 to Jan 1 0:0:0 is 31*86400 under
UTC always. If you are an astromomer this is of course a disaster since
there were actually  one more second there, but UTC does not care.
Astronomers do not use UTC.


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