[plt-scheme] GMT date stamps and time-zone-offset

Time is an ill understood concept by itself.
First there is our own feeling that time is directed to which we call the 
future.
Time is measured by counting cycles such as
- the daily cycle of the sun
- the yearly cycle of the midday highest angle of the sun
- the about montly cycle of the moon
- atomic or nuclear clocks (which count cycles too)
An ever reappearing problem is matching these cycles on each other, which it not 
trivial, because a year is not an integral number of days nor an integral number 
of mooncycles. Time is not the only subject of this problem. The same problem 
arises in the theory of the harmonics of music. The octave is well defined, but 
there is no multiple of quints that add up to a multiple of octaves. Musiciens 
speak about adding harmonic intervals, but in fact adding two harmonic intervals 
is multiplting two ratios of frequencies. For example: there is no couple of 
integer numbers n and m such that (exactly) q**n=2**m, where q is the frequency 
ratio of a pure quint (2/3) and 2 that of an octave and ** the exponentiation 
operator.  (btw, a frequency of sound is measured by counting cycles in the time 
span of a wider cycle, such as a second) Moreover: how do we define time or how 
can we know that a pendule takes the same (abstract) time for every cycle? In 
physics attempts has been made to clarify the feeling that time is directed to 
future. Nevertheless all fundametal physical laws are symmetric under time 
reversal. And whenever possible, physics people try to elimiate time from their 
formulas.
In short: not understanding leap seconds is the beginning of understanding, or 
at least appreciating the wonders of time.
Cheers, Jos Koot

----- Original Message ----- 
From: "Jens Axel Søgaard" <jensaxel at soegaard.net>
To: "Geoffrey S. Knauth" <geoff at knauth.org>
Cc: "PLT-list" <plt-scheme at list.cs.brown.edu>
Sent: Thursday, August 23, 2007 7:03 PM
Subject: Re: [plt-scheme] GMT date stamps and time-zone-offset


> Thanks Richard and Geoffrey,
>
>> On Aug 19, 2007, at 13:16, Jens Axel Søgaard wrote:
>>> The function seconds->date-string below is supposed to
>>> return a data stamp using GMT. At first I thought I
>>> were to adjust for summer time, but it seems that
>>> happens automatically. But to be on the safe side, I'd
>>> appreciate, if you try running the snippet below.
>>
>> I ran your code on 370.6-svn25jul2007 [3m] and got:
>> "Sun, 19 Aug 2007 20:56:41 GMT" -- which is correct.
>>
>> I would have expected UTC (modern) instead of GMT (traditional).
>
> I need the time stamp in a setting where GMT is expected.
>
>> I never understood why UTC has to be an anagram for both Coordinated 
>> Universal Time (English) and Temps Universel Coordonné (French).  I suspected 
>> it was a compromise to make the English and French equally miserable, and 
>> Wikipedia says as much.
>
> :-)
>
>> "Coordinated universal time a été abrégé en UTC, au lieu de CUT correspondant 
>> à l'acronyme en anglais ou de TUC correspondant à l'acronyme en français. En 
>> effet, si les experts de l'UIT étaient d'accord pour définir une abréviation 
>> commune à toutes les langues, ils étaient divisés sur le choix de la langue. 
>> Finalement, c'est le compromis UTC, nécessitant un effort des deux parties, 
>> qui fut choisi." [1]
>>
>> Geoffrey  (planetarium lecturer in the 1970s)
>>
>> [1] http://fr.wikipedia.org/wiki/Temps_universel_coordonné
>
> The subject of time has to put it mildly been convoluted. To me the
> most curious time related concept is leap seconds.
>
> -- 
> Jens Axel Søgaard
>
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