Re: [LEAPSECS] time zones and DST
On Tue, 6 Jan 2009, Rob Seaman wrote: Your April Fool's post on risks may be the most coherent analysis I've read on the subject [of DST]. Thanks :-) Where I grew up in the U.S. mid-Atlantic states, the most obvious effect of DST was to extend the usable hours of daylight for Summer evenings. (Perhaps some other narrative applies at higher or lower latitudes?) Same everywhere as far as I can tell. Since we were off school, the morning issues were meaningless. And workers go to work when their bosses tell them to. The time they own for themselves and their families is after work. Right. People generally prefer to use their evenings for recreation rather than socializing in the mornings before work. Hence shifting work closer to sunrise in the summer to get lighter evenings at the expense of the less-used mornings. If you read David Prerau's history of DST it becomes clear that it isn't possible to get bosses to agree on an earlier summer timetable except by changing the clocks. http://www.seizethedaylight.com/ DST became popular in the 20th century because of the increase in urbanization and the consequent increase in the time-related coupling of our activities. This made it harder for individuals and organizations to set their timetables according to their own preferences. The number of organizations makes it impossible to get consensus on a co-ordinated timetable change, so it has to be done by the government dictating when to change the clocks. 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. Recently, all discussions of DST are framed in turns of energy. As you say, that is a red herring. It's similar in that respect to the arguments made in Scotland (where winter days are not long enough for daylight to cover both the morning and evening commute) about the relationship between accident rates and choice of time zone. Whenever an English politician suggests switching to CET to match the continent, the Scots insist they will stay on GMT because they say children will get hurt on the roads going to school. In truth, being on GMT means the accidents happen in the evening instead, and the real reason for resisting change is they prefer the sun to rise before work. (The efficiency argument may have had some merit for war economies, but DST would have been discarded in peacetime like other war measures were it not popular for reasons other than efficiency.) If DST were really a mechanism for managing our natural daylight resource, rather than a naive attempt at PR regarding petroleum resources, it would be applied in the Winter when the daylight is in shortest supply. Your phrasing there makes it sound like you think DST increases the supply of daylight. Obviously it doesn't. It just improves the match between our timetables and sunrise, reducing the amount of wasted light in the early morning. There's no wasted light in winter mornings, so it doesn't make sense to have DST then. Having said that, there is a general tendency for time zones to move so that they are centred further west than their nominal meridian. The Central European and North American Central time zones are good examples. This has the effect of making sunrise later in the winter than it would otherwise be, in those areas near the edges of the time zones - that is, a kind of winter DST, though often with even more DST in the summer. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ ROCKALL MALIN: SOUTHERLY IN SOUTH AT FIRST, AND BECOMING VARIABLE 4 IN NORTH FOR A TIME, OTHERWISE MAINLY WESTERLY OR SOUTHWESTERLY, 4 OR 5, OCCASIONALLY 6. MODERATE OR ROUGH. OCCASIONAL RAIN. MODERATE OR GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] time zones and DST
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. 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. I continue to question whether DST is the right platform for accommodating secular shifts in the underlying worldwide civil timescale. Some sort of longitudinal study would be required to build a case for any solution that doesn't stabilize the timescale. Your phrasing there makes it sound like you think DST increases the supply of daylight. 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. 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. The Earth is very asymmetric north and south and such a study would be likely to reveal interesting usage patterns relating to underlying human factors. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] time zones and DST
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 d...@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. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
