Re: [LEAPSECS] The real problem with leap seconds

From: Ed Davies <ls_at_EDAVIES.NILDRAM.CO.UK>
Date: Fri, 13 Jan 2006 15:05:02 +0000

Michael Deckers wrote:
>> ....
>> Sort of like, is it a particle or a wave? :-)
> At the risk of being misunderstood as sarcastic: if
> users of UTC were really expected to understand such
> strange concepts (Schrodinger time) I would plead for the
> immediate abolishment of UTC. Why cannot UTC be simply taken as
> the reading of a clock that runs at the same rate as TAI and
> that is is set back by a second every once in a while?

Not really Schrodinger time - just time which you can usefully
think of in different ways for different purposes.

UTC can be taken the way you suggest most of the time (and
that's clearly the way TF.460 wants to think of it), but it
is then not well defined during the leap second itself. To
deal with that properly you have to either:

1) think of a count of UTC milliseconds or whatever (including
those in the leap second) which is then the same as TAI or

2) work in separate fields with a 61 second minute.

>> The truth is that UTC only really makes sense as a year,
>> month, day, hour, minute and second value. Years have 12
>> months, months have 28, 29, 30 or 31 days, days have 24
>> hours, hours have 60 minutes, minutes have 59, 60 or 61
>> seconds.
> Then why can the IERS express UTC in the MJD notation?

We've recently had a question about this on this list which
wasn't answered clearly. MJD 27123.5 means 12:00:00 on day
27123 if it's not a leap second day, but what does it mean
on a day with a positive leap second? 12:00:00.5? I think
it only works if that level of precision doesn't matter but
maybe some document somewhere has a convention.

Thanks for the further notes from TF.460.

Received on Fri Jan 13 2006 - 07:07:00 PST

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