Why isn't the beginning and the ending of DST equally spaced from the
summer solstice?  There are approximately 11 weeks (April 1st to June
21st) before, but 17 weeks (June 21st to Nov 1st) after the summeer
solstice.  If having a certain amount of daylight is good or beneficial (ie.
reducing crime & auto accidents, enjoying the end of day, being more
productive, etc.) why isn't there an equal amount of DST on both sides
of the summer solstice?  I don't believe "politicans have no
common sense" is an acceptable answer. Thanks.

ifiamnotiwhowillbe,

The basic framework for Daylights Savings Time was set by The Uniform
Time Act of 1966, but has been altered a couple of times since, most
recently in 1986. As originally conceived, Daylight Savings Time began
on the last Sunday in April, but in 1986 was changed to the first
Sunday.  The reason for this, as given by the California Energy
Commission is as follows:

"This was done ostensibly to conserve energy during the month of
April. Adding the entire month of April is estimated to save
nationwide about 300,000 barrels of oil each year."

So I imagine that extending Daylight Savings Time into November would
not have the same rate on return of saving energy in exchange for
losing morning daylight, and thus its extention was not necessary. 
But these times have been changed in the past during certain crises,
and if, for example, a war with Iraq were to provoke another energy
crisis, it is possible that Daylight Savings Time may be changed once
again to provide more relief.

Sources cited:

  End Daylight Savings Time
  http://www.standardtime.com/

  Daylight Saving Time - Saving Time, Saving Energy
  http://www.energy.ca.gov/daylightsaving.html

  Daylight Time
  http://aa.usno.navy.mil/faq/docs/daylight_time.html

Google search terms used:
  reasons for daylight savings time
  daylight savings time 1986 change

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Request for Answer Clarification by ifiamnotiwhowillbe-ga on 02 Nov 2002 05:48 PST

I do not consider that you have answered my question! (But then what
should I exspect for $2?)  You gave a history of what the politicians
did, but not the WHY!!!  Why isn't the # of weeks of DST the same
before as well as after the summer solstice?

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Clarification of Answer by hailstorm-ga on 02 Nov 2002 17:04 PST

ifiamnotiwhowillbe,

According to Senate deliberations in 1986, there were thoughts of
extending the end of Daylight Saving Time into November. But the
arguements given against it were that Midwestern schoolchildren would
have a more dangerous trek to school in the morning, and that farmers
would lose valuable working time during the harvest season. The latter
reason is the only one that would affect the November time period. 
Because the combined determents of DST were more pronounced in the
fall than the spring, it is considered better to extend it just in the
spring time period, rather than equally in Spring and Fall.

To read the deliberations in more detail, please see
http://www.senate.gov/~rpc/rva/992/992104.htm

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Request for Answer Clarification by ifiamnotiwhowillbe-ga on 08 Nov 2002 08:43 PST

Hailstorm -  Thanks for trying to clarify the situation, however, for
me, it confuses it further.  If they extended DST further into
November it would make the problem that much worse (ie it would be
more asymetrical than it is now).  They should stop DST approx. Sept
15 in order to give the school children the same amount of daylight
(11 weeks), (except for Carniegie's comments below).

Or did I misunderstand what you were saying?

Thanks again,
Steve

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Clarification of Answer by hailstorm-ga on 08 Nov 2002 15:45 PST

ifiamnotiwhowillbe,

What I was attempting to say is that, according to Senate
deliberations, the reason for the asymetry of the current Daylight
Saving Time is to allow farmers more daylight time during the Fall
harvest season. Because there is no harvest (or at least considerably
less harvesting) done during the Spring, it was considered better to
lengthen Daylight Saving Time only during the Fall season, rather than
equally both ways.

---

Request for Answer Clarification by ifiamnotiwhowillbe-ga on 11 Nov 2002 06:17 PST

Hailstorm, 
Thanks! While I believe that there some truth to what you say about
the harvest, from what I have read the farmers didn't really want DST.
They are used to getting up at any hour to get done the work that
needs to be done.  Certainly in todays age(headlights on tractors,
etc.) they can and do harvest all night long - if the weather is good.
I don't know if Ihave to give an "OK you have answered my questions"
for you to get your $2, but condsider I have said it as you have
certainly earned it.  That said, if you ever find out any more, please
let me know through this channel.
Again, many thanks!
Steve

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Clarification of Answer by hailstorm-ga on 11 Nov 2002 16:42 PST

ifiamnotiwhowillbe,

I'm sorry the answer was not to your satisfaction. If I come across
more definitive information on this subject I will post it here.

Daylight saving time could start March 1st, but the northern 2/3 of
the North Temperate zone typically experiences temperatures as low as
-39 degrees f = -39 degrees c at 6 am all of March, when some people
need to leave for work and school. In these locals early November
mornings are about as warm (or cold) as early March mornings. I agree
March 1st would be an improvement for sub tropical locations such as
Florida. I think you agree, it would be confusing if about 1/4 of the
States/countries started day light savings time a month sooner. Do
tropical counties have daylight saving time?  Neil

Neil, thanks, you have some interesting points!

It would be interesting to know what the population of the N 2/3 of
the North Temperate Zone is compared to the South 1/3.  The NTZ
extends from 23.5°N to 66.5°N  latitude, therefore 2/3  (37.8°N) would
run a little south of a line between San Fran, Denver, St. Louis, &
D.C.........I am quessing that the population would be about equal,
and it is population that we should be concerned with not land
area....... or is it?  Perhaps the more weeks of DST after the summer
solstice is for harvesting purposes of the Great Plains?!?!?!  But I
thought that the farmers didn't like DST at all because theye are use
to working when the sun shines no matter what the clock says.....and
besides now many of them work at night with good lighting.

Also you say "NTZ......typically experiences....as low as- 39 degrees
fat 6 AM all if March.....".  -39° certain isn't the average
temperature for the entire 2/3 of the NTZ.

If what you say is correct why isn't it called "temperature degree
saving time"?

Many thanks again,

Steve

PS  I am still looking for a "better" answer!

Dear Steve "ifiamnotiwhowillbe",

I don't think I have noticed this asymmetry before, but now you
mention it I've thought about it and I think I've found your answer. 
In fact, I've found two answers: I don't think much of my first
answer, but I'm pretty sure that the second one is the real McCoy. 
Some of what I say here differs depending on which hemisphere you are
in; for the sake of explanation, I'll talk about the northern
hemisphere.

First, Neilzero talks about the relevance of temperature.  In this
context it is worth noticing that there is some inertia in the effect
of the variation of day length and apparent position of the sun in
influencing ambient temperatures: it takes some time for the effect of
these changes to heat up or cool down weather systems.  So the coldest
part of winter is not at the winter solstice but rather (in the
northern hemisphere) in January or February, and the hottest part of
summer is likewise later than the summer solstice, in July or August. 
So if temperature were relevant, you would expect the daylight saving
period to be asymmetric about the summer solstice, in the way that you
note it is.  But I don't think this is really the issue, and I suggest
you read on to my second point.

The real culprit is the so-called Equation of Time: let me tell you
all about this.  The length of the day varies at different times of
the year.  You'll be saying "I know that: that's what the question is
all about."  But no: I don't mean here that the length of the daylight
part of the day varies (as we all know it does) but that the actual
length of the entire day-plus-night is not the same throughout the
year.  Most days, in other words, are not exactly twenty-four hours
long.  To understand what I'm suggesting, imagine that you were to
determine noon on two consecutive days by the sun by observation - by
noting the moment when the sun was highest in the sky.  You would find
that the intervening period, as measured by any terrestrial,
non-astronomical clock, would be near twenty-four hours, but not
necessarily exactly so. Twenty-four hours is just the average length
of a day.

It's worth noting here that this is why Greenwich Mean Time is so
called: the word "mean" refers to a clock based on the _average_
length of a day, not the actual length of each day.  (All normal time
systems are based on mean solar time, of course, not just that of
Greenwich.)

There are two reasons why the total day length varies from the mean. 
I'll explain what they are, though it's worth mentioning that to
understand my conclusions you don't need to understand all this, but
merely to accept the end result.  The first reason is that the earth's
orbit around the sun is not circular but elliptical (though very
nearly circular).  The earth, then, is sometimes further away from the
sun (in the northern hemisphere's summer, in fact) and sometimes
nearer.  Its angular velocity around the sun varies and this produces
a small change in day length.  As you would imagine, the period of
this variation is one year.

The other effect is due to the fact that the plane of the earth's
rotation is tilted with respect to its orbit around the sun.  Yes: you
knew that - that's why we get seasons at all, of course.  But this
also produces small variations in total day length, this time with a
period of six months: there are two cycles of variation per year.

These two effects, with different periods, combine to produce a
complex pattern of variation throughout the year.  The two effects
interfere constructively (as the physicists would say) and produce the
most noticeable result at the turn of the year.  At this time, the day
length is less than twenty-four hours and the period of daylight in
each day occurs earlier in clock time than the previous day.  You may
have noticed (or you can easily check) one obvious effect of this:
that, although the length of daylight obviously starts to increase
again immediately after the winter solstice, the time of sunset
continues to move _earlier_ (the opposite of what you would expect)
for some days - until well into January.

Note that, although these effects are small, they are cumulative, so
that the difference between solar time and solar mean time is not
always small.  In fact, the cumulative effect means that in the
extreme case - around 4 November - the sun is going through its paces
as much as sixteen minutes earlier than you might imagine if you
didn't know about all this and thought it followed your clock's mean
time.

For a fuller explanation, see the web site of the Royal Observatory,
Greenwich - part of the site of the National Maritime Museum at

http://www.nmm.ac.uk/server.php?request=setTemplate:singlecontent&contentTypeA=conWebDoc&contentId=351

The two separate effects are shown in the diagram at

http://www.nmm.ac.uk/uploads/gif/EoT1.gif

and the sum of the two effects - the difference between solar time and
solar mean time throughout the year - the "Equation of Time" itself at

http://www.nmm.ac.uk/uploads/gif/EoT2.gif

If you'd like to see all the mathematics, see

http://www.analemma.com/

Now what has this all got to do with daylight saving?  Well, I think
we have to look at what determines why many communities change to and
from daylight saving time during the year.  The point of daylight
saving time, of course, is to make use of the extra daylight it gives
in the evening (as measured by clock time).  But this would be useful
in the winter too, so why do we revert to standard time?  Simply
because the time of sunrise would be unacceptably late if we didn't,
so it's the time of sunrise that determines the dates of change.

As you will see from the diagram, at the end of daylight saving time
(at the end of October) the sun is going through its paces about 15
minutes earlier than it would be if it were not for the effects I have
described.  So - in particular - sunrise is 15 minutes earlier by the
clock that we might imagine.  And it's possible to delay returning to
normal clock time because of this.  Conversely, at the beginning of
daylight saving time (early April in the US, late March in Europe)
sunrise is anything up to 3 minutes later than expected, and the start
of daylight saving time should be delayed slightly to compensate.

So how much delay is necessary?  Well, that depends on your latitude,
so things get complicated.  The combined difference of perhaps 18
minutes in the apparent time of sunrise is equal to the change in the
time of sunrise in spring or autumn in temperate latitudes of about
ten to fifteen days, so this would explain an asymmetry of two weeks
or more, but perhaps not all of the five weeks (in Europe) or six
weeks (in the USA) that seems to be the case.

I hope this helps.

Carnegie

Carnegie, 
Thanks!  I like your first answer best, except it should be called
degree savings time.  I thank you for the 2nd answer as you exposed me
to much new information/knowledge which I find fascinating.  Are you
saying in the 2nd answer that the approx 15 minutes to make up are off
set by the extra 6 weeks of standard time in feb & march?  If so why
do we add an hour to make up 15 minutes?

It would be interesting to find the correct answer instead of these
intelligent guesses.....to find out what the politicians were thinking
(or not thinking) when they set it up....or who advised them and what
their reasoning was.  Thanks again all of you.
steve

Dear Steve "ifiamnotiwhowillbe",

Thanks for your comments.

You ask "Are you saying in the 2nd answer that the approx 15 minutes
to make up are off set by the extra 6 weeks of standard time in feb &
march?"  Well, I'm not sure I know what you are asking.  I certainly
haven't explained the full six weeks: as I said, my suggestion is that
the Equation of Time effect accounts for only about two weeks or so of
the asymmetry.

Let me say what I mean another way.  I explained it before by saying
that the variation between solar time and solar mean time means that
the sun doesn't follow the clock exactly.  Another way of saying this,
of course, is that our clocks don't follow the sun exactly.  At the
beginning of daylight saving time, our clocks (following solar mean
time) are within two or three minutes of solar time.  But at the end
of daylight saving time our clocks are running a quarter of an hour
slow according to the sun.  So although we kid ourselves as the
changeover date approaches in October that we are still using a clock
time one hour ahead of solar time, we are actually using a time only
around three-quarters of an hour ahead of solar time - the hour we
changed in the spring less the fifteen-minute difference between solar
time and clock time in late October.  So we have already set our
clocks back a quarter of the required change already (relative to the
sun) - without touching anything!

Now it should be clear that if we used, say, what has been called
double summer time, where the clocks are put two hours ahead instead
of one, we should be able to maintain that only for a shorter period
of summer, for fear of creating unacceptably late sunrises as measured
on our clocks.  And conversely the fact that by late October we are
actually running only three-quarters of an hour ahead rather than the
hour that it appears means that we can keep that time for longer
without creating the dark mornings that we don't want.  At the rate at
which sunrise is changing naturally at that time of year, this
dispensation allows us to postpone the change by another two weeks or
so (depending on latitude).

You say "It would be interesting to find the correct answer instead of
these
intelligent guesses.....to find out what the politicians were thinking
(or not thinking) when they set it up....or who advised them and what
their reasoning was."  I suspect that there is no answer to this and
that you have clearly spelled out why.  If a number of advisers were
involved and then a number of politicians (even in one jurisdiction)
and then, no doubt, a number of later processes of change or at least
consideration of change, there will have been very many different
theories and opinions which went into making the decisions that have
led us to where we are now.  If different politicians, for example,
vote the same way for different reasons, there can be no answer to
your question.

Sorry about this!

I trust this helps.

Carnegie

Carnegie,
Your further clarification did help and I thank you much for all of
your input on all aspects of the subject. I appreciate it.
Steve

I just believe this rating of the answer is completely uncalled for.
It's a 2$ question with the most accurate answer known to man. Rate
the question in respect to the pricing and take the adolescents
elsewhere is what I believe.