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Tampering with Time


What's the time Mr. Wolf? I remember very well as child playing this game with my contemporaries. I also recall being taught at school in my infancy how to tell the time - read the face of the clock, in other words. So, what's it all about? Why, when astronomers have gone to great pains to give us the means to order time such that our mechanical (or electronic/atomic) clocks keep faith with the Earth's rotation and its movement about the Sun, do we mess about with the clocks the way we do each year?

What do we understand by the terms noon and midnight? Once I might have assumed that most people would associate noon with that moment when the Sun is on the local meridian and at its highest in the sky for the day. But anybody with a well set up sundial may confirm that noon by the clock on the mantelpiece is mostly at variance with the sundial. When we measure or (better) calibrate time, what we are doing is devising a means to reference our activities to the state of daylight. This is all too obvious because the argument for putting the clocks forward is to enable us to have more daylight of an evening, or during the after noon (p.m. - post meridiem) period. Of course we do not increase the over all availability of daylight; mankind has not yet succeeded in meddling with the Earth so as to enable this to happen at the press of a button or the throw of a switch. Instead we light the night sky with artificial lamps and throw away the dark, but that's another matter.

By putting the clock forward one hour all we are simply doing is displacing the perception of midday (or thereabouts) to occur when the clock reads 13h 00 instead of 12h 00. It has already been noted that true noon, or the Sun's or sundial noon if you prefer, and clock time or mean time, only concur four times during the course of a single year. The difference in the reading between the two is called the equation of time. This has to do with the Earth's motion and the shape of its orbit about the Sun - hence the astronomer's input.


Put the question, why the necessity for this clock tampering? If it has to do with our working habits why not arrange the times we choose to start and end work for the day to be in harmony with the clock, why the other way about? Surely, if we require to have more light of an evening why not just start the working day earlier by one hour (or whatever is deemed acceptable) and knock off one hour earlier? Many indeed do just that.


Time zones are managed quite adequately in large countries and subcontinents. This becomes necessary due to the significant differences in longitude over these landmasses. It would seem obvious from this standpoint that the most convenient time at which to have midday anywhere would be when the Sun is close to the local meridian, in other words at 12 noon. If the argument for having permanent summer time is because of greater political integration with Europe, just take a look at an atlas.

The Greenwich meridian is still used as the prime reference for longitude and hence for time calibration - GMT or Universal Time (UT) as it is now called. That meridian places Spain, the western coastal fringes of France and the bulk of the British Isles, including the Republic of Ireland, west of the datum line. Of course the more we integrate politically and economically with Eastern Europe the more distant will these areas be from the Greenwich meridian.

But longitude is not the only factor. It is indeed latitude that determines the overall amount of light available from the Sun during the course of a day. Above the Arctic Circle the Sun does not even rise above the horizon for some of the winter. (Sizeable areas of Norway, Sweden and Finland fall into this category.) In winter here in the Northern Isles the hours of natural daylight are significantly shorter than in England where the British parliament sits.


It is argued that road accidents occur more frequently during the hours of darkness. Just so, those of us in northern latitudes, especially in rural areas, find travelling in dark mornings less acceptable than travelling at night. If the clocks were to remain set at so-called summer time throughout the year it does not need me to point out that we would suffer this disadvantage throughout the months of winter.


Longitude is of no great significance for most of Britain. The outer Hebrides are some 24 minutes of time to the west of the Greenwich meridian, which means that already  their evenings are apparently lighter (and mornings proportionately darker) when clocks are set to UT (GMT).

Therefore, I would argue that it makes proper sense to have our clocks set to read in conformity with mean solar time. In this way noon and midnight, as indicated by our clocks, will be close to the truth of the situation. To have clocks set forward one hour or even two (as in double summer time) panders to the same mentality as public house clock time (set forward as a period of grace before throwing out time!). In other words, we appear incapable of managing our affairs without debasing time and fooling around with the clocks.


(John Vetterlein spent some of his professional career working in the meridian and time departments of astronomical observatories. He is presently researching the upper atmosphere from Rousay.)



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