tudorsailor
Well-Known Member
How is it that British Summer Time starts 14 weeks after the shortest day, but ends 7 weeks before the shortest day. Why is it not equal?
Just curious
TS
Just curious
TS
Timing of clock changes is unequal. Why?
- Thread starter tudorsailor
- Start date
BruceDanforth
Well-Known Member
It's arbritary. Why should it be equal?
alan_d
Well-Known Member
Because if the aim is to maximise socially-useful daylight one would expect this to be approximately symmetrical around the solstice.
VicS
Well-Known Member
It's because the earth's orbit around the sun is not circular it is roughly eliptical and the earths distance from the sun is less at one end of the orbit than at the other
The longest and shortest days don't coincide with when the earth is at its futhest or nearest points to the sun ( that's aphelion and perihelion) but rather when the inclination of the earth's axis is greatest towards and away from the sun.
That occurs at the points in the orbit where the rate of change from the small radius at the ends of it major axis and the large radius and the ends of the minor axis is at its greatest..
Ok summer time starts 14 weeks after the shortest day but the corresponding change in the geometry as the earth leaves the tighter curved part of the orbit is only 7 weeks.
Hope you can follow that. Not easy to explain.
Don't quote me I may not have all the detail exactly correct.
The longest and shortest days don't coincide with when the earth is at its futhest or nearest points to the sun ( that's aphelion and perihelion) but rather when the inclination of the earth's axis is greatest towards and away from the sun.
That occurs at the points in the orbit where the rate of change from the small radius at the ends of it major axis and the large radius and the ends of the minor axis is at its greatest..
Ok summer time starts 14 weeks after the shortest day but the corresponding change in the geometry as the earth leaves the tighter curved part of the orbit is only 7 weeks.
Hope you can follow that. Not easy to explain.
Don't quote me I may not have all the detail exactly correct.
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guernseyman
Well-Known Member
Just a guess - the temperatures in the autumn permit outdoor activity longer after the solstice than before the solstice in the spring.
BruceDanforth
Well-Known Member
I'm guessing you mean an equinox.
pugwash60
Well-Known Member
In the Navy when adjusting clocks they use the 'stuff up the workers' principle, so when going West and the clocks go back they do it during the day so work carries on for an extra hour, and when heading East and clocks go forward they do it during the night so you start work an hour earlier.
Whilst this isn't exactly relevant I suspect that it's more for the convenience of various departments than for strictly astronomical reasons.
Whilst this isn't exactly relevant I suspect that it's more for the convenience of various departments than for strictly astronomical reasons.
alan_d
Well-Known Member
I don't see why the fact that currently perihelion is about a fortnight after the solstice is relevant. The point is Daylight Saving, and length of daylight is to a close approximation symmetrical about the solstice.
Sybarite
Well-Known Member
I would like summer time to be retained. The argument against it is that children going to school in the North of Scotland would be going very much in the dark. But why cant their schools begin at 10am?
BruceDanforth
Well-Known Member
Why should things be more inconvenient for them in preference to you though?
Nobody gets any more hours of daylight.
Nobody gets any more hours of daylight.
duncanmack
Well-Known Member
Timing of clock changes is unequal. Why?
It's organised by the government.
Nuff said.
It's organised by the government.
Nuff said.
VicS
Well-Known Member
Taking the first point, It's not relevant! Ignore that paragraph of my post if it's confusing.
Taking the second point. The period over which daylight saving is applies is not symmetrical about the summer solstice. That the whole point of the OPs question. He referred to the winter solstice but there are similar unequal periods before and after the summer solstice. By simple arithmetic what applies to one solstice applies to the other. (DST is approx 12 weeks before to 19 weeks after the summer solstice)
Ex-SolentBoy
Well-Known Member
I heard that 90 % f the population don't think we should change at all. But most Scots like the change.
However, as the Scots punch over their weight in the UK parliament, and monopolise their own, us southerners cannot really complain.
Democracy at work- go figure!
However, as the Scots punch over their weight in the UK parliament, and monopolise their own, us southerners cannot really complain.
Democracy at work- go figure!
DaveRo
Well-Known Member
If the objective of DST is 'save' the 'wasted' daylight at the start of the day then the dates ought to be related to the time of sunrise, not the length of daylight. The earliest sunrise occurs before the summer solstice - up to 2 weeks, depending on the location.
This might explain why it's not symmetrical about the solstice - but I suspect that the actual dates are a compromise between countries, and may depend on their traditional holiday periods.
This might explain why it's not symmetrical about the solstice - but I suspect that the actual dates are a compromise between countries, and may depend on their traditional holiday periods.
Bilgediver
Well-Known Member
On our ships the clocks were adjusted so that noon was always after lunch in order that it didn t interfere with the mates attending the lunch table at 12
The change done on the night watches.
prv
Well-Known Member
On our ships the clocks were adjusted so that noon was always after lunch in order that it didn t interfere with the mates attending the lunch table at 12
The change done on the night watches.
On the voyages I've done, it wouldn't have been changed at night because people would have moaned at unequal length night watches. When to change it during the day was subject to a surprising amount of Wardroom discussion, but ultimately tended to be decided based on what the cook had in mind for lunch and dinner and how long he needed to prepare them.
Pete
cliffordpope
Well-Known Member
The people who really believe that adjusting the clocks increases the length of sunshine must be same who thought that adding a "0" to every telephone number would create thousands of new numbers.
Leave it at GMT all the year round, and let people in Scotland or Cornwall or East Anglia do what they like. If it suits the schools to start earlier, or later, just do it. Why does it need national legislation to get organisations to alter their working hours in winter?
Why don't schools have longer days in summer than winter, for example?
Leave it at GMT all the year round, and let people in Scotland or Cornwall or East Anglia do what they like. If it suits the schools to start earlier, or later, just do it. Why does it need national legislation to get organisations to alter their working hours in winter?
Why don't schools have longer days in summer than winter, for example?
Dockhead
Well-Known Member
One of the great questions of our age.
One proposal was just to leave the clocks set like that. Why bring down doom and gloom on the world just when the daylight is fading anyway?
Or we could simply get up and start work an hour earlier, so there's more daylight left at the end of the day.
One proposal was just to leave the clocks set like that. Why bring down doom and gloom on the world just when the daylight is fading anyway?
Or we could simply get up and start work an hour earlier, so there's more daylight left at the end of the day.
