[ntp:questions] Leap second to be introduced in June

fm at fr.invalid fm at fr.invalid
Mon Jan 19 11:38:31 UTC 2015

William Unruh <unruh at invalid.ca> wrote:
> On 2015-01-19, Mike S <mikes at flatsurface.com> wrote:
>> On 1/18/2015 6:04 PM, William Unruh wrote:
>>> UTC always has 86400 seconds per year.
>> You clearly don't understand how leap seconds work. You're embarrassing 
>> yourself now. When there's a leap second, there are 86401 SI seconds in 
> I AM clearly embarrasing myself, since 86400 is the number of seconds
> per SAY not year. Slight difference!
> Of course there are 86401 seconds in a day including a leap second. But
> UTC only sees 86400. It forgets about one of them. 

I am not sure what you mean by "sees", but I cant figure a meaning
that would be compatible with the fact that UTC clearly identifies 
86401 seconds on the day the leap second occurs.

Maybe the confusion arises from considering UTC dates as 
"time interval" quantities, which they are not, rather than timescale 
readings. TAI days have 86400s, UTC days may have 86401 seconds ; 
so it happens that when TAI reads 00h00:00, UTC reads 23:59:60. 
That is what makes computing time intervals more complicated in 
UTC than in TAI but neither TAI nor UTC is defined by the number
of seconds elapsed since an epoch.
François Meyer

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