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<p><font size="+1">The vast majority of astronomical data that
reference Universal Time cannot be said to be UT1. If a data
product does not trace back to UTC, then UT is the only
appropriate default choice. This is similar to not preserving
more decimal places than supported by input arguments, or not
overreaching on units by reporting microseconds when millisecond
or second accuracy is appropriate.</font></p>
<p><font size="+1">Indeed, most UT1 values in recent decades would
have resulted from applying the DUT1 correcting to UTC, and
would only be precise (and hopefully accurate) to 0.1 seconds.
But more frequently the values represent the generic notion of
Universal Time (UT) and handling of leap seconds or precision
traceability back to a reference clock as would be needed to
claim conformance to the UTC standard are neglected.<br>
</font></p>
<p><font size="+1">Rob</font></p>
<p><font size="+1">--</font><br>
</p>
<div class="moz-cite-prefix">On 11/29/18 2:01 AM, Markus Demleitner
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:20181129090119.k3argncc43moqatp@victor">
<pre class="moz-quote-pre" wrap="">Hi Steve,
On Wed, Nov 28, 2018 at 08:12:06PM -0800, Steve Allen wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">On Tue 2018-11-27T13:23:50+0100 Markus Demleitner hath writ:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">A pre-built PDF is available on
<a class="moz-txt-link-freetext" href="http://docs.g-vo.org/timesys-draft.pdf">http://docs.g-vo.org/timesys-draft.pdf</a>, the source is still available
from
<a class="moz-txt-link-freetext" href="https://volute.g-vo.org/svn/trunk/projects/time-domain/timesysnote">https://volute.g-vo.org/svn/trunk/projects/time-domain/timesysnote</a>.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
Table 1
I strongly object to the notion that the term UTC shall be used for
time stamps that were originally labelled as GMT. The term used for
that should be just plain UT.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
Ok -- I agree UTC was a bad choice for labelling "historical data
taken in GMT".
I'd still like to keep the number of (initial) terms as low as
possible, and I'd expect if we let people choose between UT and UT1,
that'd not help overall, and I'd still like to escape a separate
"GMT" time scale if possible.
So -- given we already have UT1 would you object to saying
"Historical data given in GMT should be annotated as being in UT1"?
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">UTC has always referred to an atomically-regulated time scale. There
[...]
The IAU directed that the catalog used for time determination changed
from FK3 to FK4 on 1962-01-01, and that caused a shift of 1.5 ms in
the values of UT that were being provided by various observatories.
The extrapolated estimates of the value of TAI at that date and before
have uncertainties and differences of similar size.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
It's clear that automatic processing can only go so far, and we
should probably set some (time-dependent) goal as to what precision we
strive for. I've hoped we could generate some rules of thumb
analogous to what Arnold has suggested for reference positions, where
we recommend (overridably) bumping the systematic errors depending on
time scale and the age of the data. Your remarks let me doubt it'll
be so simple... ah well.
Thanks,
Markus
</pre>
</blockquote>
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