[LEAPSECS] time zones and DST

[Tony Finch]

On Tue, 6 Jan 2009, Rob Seaman wrote:

> Tony Finch wrote:

>

> > This is why DST is a sensible solution to the problem of the mismatch

> > between natural human preferences and inflexible timetables based on mean

> > solar time.

>

> I don't think "inflexible" is the right choice of words, but I'll let it pass

> to make a more basic point.


The individual timetables aren't inflexible, but the aggregate of all of
them is.


> DST only offers the opportunity for sensible seasonal solutions.  In the

> absence of coherent government oversight (an oxymoron if ever there

> was), no such solution will be sensible.


Right. Prerau's history provides plenty of examples.


> No, just that the pressure to do the job right is greater when the

> resource is in shorter supply.  Since DST is actually applied precisely

> when it spills over both further into the morning and further into the

> evening hours, I question whether your explanation is complete or

> consistent.


Don't be confused by the name: it isn't about "saving" daylight. Winter
time already makes best use of daylight when there's less available.
In the summer there's more daylight, but the early morning daylight is
wasted, so we move the clocks so that we can make better use of the extra
light.

DST can be viewed as a version of my "sunrise time" idea that has been
simplified so that it's acceptable for practical use - i.e. roughly
adjusting clocks to follow sunrise rather than noon, which has the effect
of giving you light later into the evening in the summer.


> > Having said that, there is a general tendency for time zones to move

> > so that they are centred further west than their nominal meridian.

>

> As with other clock and calendrical issues, there is rather a tendency to

> overgeneralize.  For instance, it would be very interesting to contrast DST

> policies in the southern hemisphere with those in the north.


Southern timezones are biased westwards for the same reason as northern
ones - the sun rises later in the west there too. It isn't a seasonal
effect so there's no north/south difference. What is different is the
calendar months in which DST is applied.

There seems to be less agreement over DST schedules in the south - they
don't have large co-ordinated blocks following the same schedule like
North America and Europe. Australia doesn't have a federal schedule, for
example. I guess this is because there aren't any similarly large highly
developed and densely poulated areas in the south.

Tony.
-- 
f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
ROCKALL MALIN: MAINLY SOUTHWEST 4 OR 5, OCCASIONALLY 6 AT FIRST, BECOMING
VARIABLE 3 FOR A TIME. MODERATE OR ROUGH. OCCASIONAL RAIN. MODERATE OR GOOD.