What is a time zone?

Alex LIVINGSTON alex at agsm.edu.au
Fri Feb 16 06:27:45 UTC 2001

At 14:43 +0000 2001-02-15, Clive D.W. Feather wrote:
>David Keegel said:
>>  I think common usage outside this group is that a time zone has variable
>>  boundaries, and is something like the set of places which *currently*
>>  observe the same time (although perhaps US EST and CDT might be
>>  considered different time zones).
>Change this to say "currently observe the same time and intend to do so for
>the indefinite future" and you eliminate that problem.

I presume by "the same time" Clive means "the same time as each 
other" and not necessarily the same UT offset. That would mean that 
Queensland would have to be considered as a separate time zone from 
the other mainland Australian eastern states (and territory), and, 
under the regimen that applied until 1999 and will possibly continue 
this year, Tasmania as yet another. The Northern Territory and South 
Australia would also have to be considered as separate from each 
other. I don't know whether Australians would see it that way in 
general. They might concede that they are different time zones while 
they are observing different times, but I doubt they would otherwise.

I assume David is thinking of Indiana, most of which is on the same 
time as the US central zone during "summer", but is still thought of, 
by many, as being in the eastern time zone. Instead of doing that, 
and ignoring Clive's amendment, one could think of the time zone 
boundary as changing twice a year. The difficulty with that, of 
course, is that, under one interpretation of such a scenario, (most 
of) Indiana would change time zone twice a year even though its 
clocks don't change.

The alternative (which seems far superior to me and is consistent 
with labelling time zones with their offset alone) is to think of 
Indiana as remaining in the same zone, the boundaries of which move 
east and west around it in an annual cycle. This accords better with 
what I imagine is the general Australian perception of a time zone. 
The North American perception is harder to sustain in Australia, 
where more than half the country in areal terms (but less than half 
in population terms) does not observe daylight-saving time. The 
geographically-based designations "Eastern Time" (ET) and "Central 
Time" (CT), each meaning whatever the time being observed in its 
respective zone is on the date in question, cannot be made to work in 
Australia. Even in North America, in order for them to work 
universally, most of Indiana, and parts of Canada, _would_ have to be 
thought of as swapping between the two zones twice a year!

I am flabbergasted at the resistance there seems to be to the idea of 
people knowing what their local offset(s) from UTC is/are. In the 
vast majority of cases such an offset is a one- or two-digit number 
with a sign, and nowhere is there a need to know more than two of 
these, in a world of 8-, 9-, and 10-digit phone numbers and post 
codes, not to mention PINs and (in the US at least) social security 
numbers! In a place where daylight saving is practised, it is simply 
a matter of knowing these two simple numbers (like one's floor, 
house, apartment, and/or room number) and knowing which one applies 
at the time, which is simply a matter of knowing whether daylight 
saving is in force or not.

Can't we time-zone whizzes (if I may be so bold as to include myself) 
allow ourselves to have a tiny bit of conscious influence, rather 
than (or as well as to start with) bending over backwards to 
accommodate the whims and follies of the powers that be? We are doing 
the world a significant favor (aren't we?); it doesn't seem too 
audacious to make it known what would make it easier for us to 
continue to do so, especially if the general population would also 
benefit (we think). Should we be deterred just because the resistance 
seems almost insurmountable? Would it inevitably threaten our 
perceived impartiality?

IT, Australian Graduate School of Management (AGSM), UNSW SYDNEY NSW 2052
Fax: +61 2 9931-9349 / Phone: +61 2 9931-9264 / Time: UTC + 10 or 11 hours

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