Re: [LEAPSECS] what should a time standard encompass?

From: Ed Davies <ls_at_edavies.nildram.co.uk>
Date: Mon, 27 Jan 2003 18:21:02 +0000

William Thompson wrote:

> There's been a lot of talk in this forum about civil time, and what it will be
> like millenia from now. I find most of that talk rather silly. What tends to
> get ignored is that changes to the UTC time standard will make themselves felt
> in the astronomical and astronavigation community not in comfortably far away
> millenia, but in mere decades. It will affect not only professional
> observatories, but millions of amateurs who don't have the resources that
> professionals have access too.

As far as astronomers, both amateur and professional, are concerned the
sole effect of dropping leapseconds from UTC would be that they'd have
to look up the difference between UTC and UT1 every few months even in
applications where currently UTC is a good enough approximation to UT1
for practical purposes.

I can't imagine there are many systems which directly work off a time
signal but don't have software which can be modified easily to apply
this offset - even if the offset is just entered manually every few
months.

If UTC drifts away from UT1 then astronomers can reasonably be assumed
to have the understanding and motivation required to deal with the
change without significant problems.

For amateurs, publishing the current offset once a month in a
magazine would be quite sufficient - though most could probably
look on a web site (USNO/IERS or whereever).

This need for simple action on the part of astronomers has to be set
against extra complication in a wide range of computer networks and
other systems which, as things currently are, should deal with leap
seconds but in many cases don't. Most programmers and users don't
know about leap seconds and, frankly, don't care.

System designers will either neglect leap seconds causing problems
(e.g., GLONASS) or bypass them by creating their own time scales
(e.g., GPS).

It can reasonably be argued that GPS should have used TAI but that's
rather beside the point as it would still have had a rather odd and
varying relationship to civil time.

Everything would be a lot simpler and more reliable if all systems
could work with a single simple "universal" time scale which:

1. Has SI length seconds.

2. Has minutes of 60 seconds, hours of 3'600 seconds and days of
   86'400 SI seconds always, not just often enough to lull testers
   into a false sense of security.

3. Has a straightforward relationship to civil time (i.e., fixed
   offsets of, usually, multiples of one hour).

If the cost of getting this is a trivial inconvenience to astronomers
and an adjustment of time zones every few thousand years then I'm all
for it.

Ed Davies.
Received on Mon Jan 27 2003 - 10:26:53 PST