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Daylight saving beyond the fading curtains

By John Ridd - posted Thursday, 20 September 2007


The issue of daylight saving is back on the agenda in Queensland. That happens periodically and no doubt will keep re-occurring until daylight saving is eventually introduced.

Born and bred in the UK I was totally used to “summer time” as it was called. I liked it and if I lived in England (or Tasmania) now would still enjoy it - and vote for it if a plebiscite were to be held on the issue. However Far North Queensland is neither England nor Tasmania in any way that is relevant to daylight saving.

First, in temperate areas there is a wide variation in the number of daylight hours. In winter it is not at all uncommon for the sun to struggle up at 8am and set again at 4pm: only eight hours of sunlight. In summer the same area would expect to have 16 hours of daylight, the sun rising at 4am and setting at 8pm.

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Under those circumstances there is an obvious opportunity to “save” daylight and hence reduce the need for artificial light usage. Move the clocks so that the sun rises at 5am clock time and sets at 9pm. Such a move is simply an efficient use of a natural resource - light.

Second, in a cool temperate climate the sun is always welcome. It both brightens the place up and injects some much needed warmth. It is a welcome friend.

In the deep tropics the sun is not a friend except in the very short winter period. For the vast majority of the year the sun is so powerful it makes doing anything outdoors unpleasant after about 7.30am. The whole place gets “cooked” - house, roads, the ground and so on. There is little cooling until the sun sets, until then you wait for that time when relief comes. And that occurs when the sun decides, not the clock. Being bombarded by a celestial heater at the rate of approximately a kilowatt per square meter is not just unpleasant it also presents a significant risk of dehydration. Above all else the sun is terribly enervating.

The various publicity campaigns, such as “slip, slap, slop”, try to emphasise that exposure to high doses of sunlight is dangerous. It is not a fluke that Queensland is the skin cancer capital of the world. The “Sunsmart School Project”, a very sensible idea, is a clear recognition that the sun is not an unalloyed blessing, but is potentially dangerous.

The time at any place on earth is determined by its longitude. For convenience and to prevent total chaos, humans have determined that any given area of land is to be “run” by the time at an agreed place. In Australia, Eastern Standard Time is essentially the “time” at longitude 150 degrees east. Sydney lies near that line so EST is correct “sunwise” for Sydney. Melbourne, because it is about 5 degrees to the west of Sydney, operates on a year-round “daylight saving” of 20 minutes - even without official daylight saving. Adelaide, about 11 degrees west is 45 minutes “behind” Sydney which is of course why that state does not operate on EST.

The first thing to recognise about Queensland is that the coast does not run south-north. From a time point of view that means that even just along the coast we have Brisbane in the southeast corner which is actually east of Sydney by about 3 degrees and is hence running at 12 minutes of daylight “losing” time - if I may make up a phrase. However, when you move up to Cairns the longitude is about 146 degrees west and is running on a permanent 17 minutes daylight “saving”. Note that there is about half an hour difference between sun noon time in Brisbane and Cairns.

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The second point to recognise about Queensland is that is has a considerable variation from the east coast to the west of the state. From a sun time point of view that means that Mount Isa is well to the west of Sydney or Melbourne and is in fact on almost the same line as Adelaide. So, inevitably it follows that Mount Isa residents operate on a permanent daylight saving of about three quarters of an hour. Furthermore the sun time difference between Brisbane and Mount Isa is roughly a full hour.

Queenslanders were supposed to be opposed to daylight saving because it would cause the curtains to fade. Sadly, I have never heard anybody actually say that, but never mind, it is a nice story that hurt nobody. Now although I know that the curtain fading idea - if it ever existed - is wrong, I know, as a scientific fact, that there really is something called The Equation of Time.

Due to the dual facts that the Earths orbit is not circular but elliptical, and the obliquity of the ecliptic, there is variation between clock time and sun dial time over each year. That variation is, in total, the result of the interaction of two sine curves due to the two facts mentioned above.

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About the Author

John Ridd taught and lectured in maths and physics in UK, Nigeria and Queensland. He co-authored a series of maths textbooks and after retirement worked for and was awarded a PhD, the topic being 'participation in rigorous maths and science.'

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