[ntp:questions] Leap second functional question

David Woolley david at ex.djwhome.demon.co.uk.invalid
Tue Feb 19 22:25:39 UTC 2008

Unruh wrote:

> there were actually  one more second there, but UTC does not care.
> Astronomers do not use UTC.

Astronomers use UT1 or higher.  These DO have variable length seconds, 
which I think was the original cause of confusion; I think they mixed up 
UT1 with UTC.

UT1 is more closely based on earth rotation time.  Leap seconds are 
introduced when the discrepancy between UTC and UT1 is getting too high 
(somewhere between half and one second).  Various time signals include 
this difference to a tenth of a second, or maybe better.

The UT1 second count is always close to the UTC second count, and so UTC 
  second counts are more useful for astronomers than TAI ones, except if 
you are using an epoch close to a leap second and measuring times close 
on the other side.

I doubt that a year actually exists in TAI.  When people talk about 
using TAI in computers, they are talking about the internal seconds 
count, not any external representation of it.

>> N

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