Date: Tue, 03 Jan 2006 15:54:32 -0700 From: Scott Long <scottl@samsco.org> To: Carlos Amengual <listas@informatica.info> Cc: freebsd-current@freebsd.org Subject: Re: freebsd-current Digest, Vol 127, Issue 4 Message-ID: <43BB00A8.8010201@samsco.org> In-Reply-To: <43BAE883.1090705@informatica.info> References: <20060103120026.EEEC916A41F@hub.freebsd.org> <43BAE883.1090705@informatica.info>
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Carlos Amengual wrote: > Poul-Henning Kamp wrote: > >> >> The astronomers know far too little about modern computing. > > > Something shared with the POSIX specifications writers. > > >> The following proposals have been aired: >> >> A) Abandon leap seconds. > > > See last paragraphs. > > >> B) Predict leap seconds further in advance. >> >> This increases the |UT1-UTC| tolerance and the astronomers >> will have to cope. >> >> Provided that the notice becomes long enough, 10 years as >> a minimum, computing problems will mostly disappear, provided >> operating system suppliers pay attention to it. > > > Leap seconds cannot be predicted reliably. If you mean having an initial > prediction and then issuing (supposedly less frequent) differential > corrections, you still have the problem, but with more confusion added. > > >> C) Make leapseconds smaller and more frequent > > > Then you loose the concept of a second and make the idea of timekeeping > impractical. If I understand correctly, you agree with that and choose > the idea of dropping the leap seconds: > > >> And finally some anti-FUD: >> [...] >> "We don't know what will break if we drop leap-seconds" >> >> We know very well what can break: Only systems which relate >> the position of extra-terrestial objects to UTC time can break. >> >> These devices are called antennas and telescopes and they are >> operated by scientists and technicians who should be more than >> able to figure out how to deal with this. > > > You are missing the sextants, and their users, which would be much more > complicated to "fix" than those telescopes. If leap seconds are dropped, > ships and planes are going to notice it sooner or later. > Pointing a telescope at an object 100 million light years away requires incredibly precise timing. Pointing a quadrant or sextant at an object 8 light minutes to 50 light years away requires considerably less precision. And, let's face it, real ships navigate via gyroscopes, GPS, and LORAN, all devices that value consistent timekeeping, not celestially accurate timekeeping. At least, that was my impression during my time at sea =-) Scott
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