This morning (or yesterday evening, for the organised), clocks across Britain were set forward one hour. This is something that has always irritated me. Why do we need to do this? If we want to make the most of light mornings, why can't we just get up earlier? Why do we need to fool ourselves into thinking that the time is an hour later than it really is?
Here's the thing that irritates me: British Summer Time is not
real. The position of the hands on a clock face are a measurement, and as such, should aim to measure as accurately as possible. But what are they measuring, exactly? Well... it gets a little more complicated than you might expect when you try to answer this question. Roughly, it's the position of the sun in the sky, but not relying on actually being able to see the sun, and extended through the hours of darkness, too. It's a measure of the Earth's rotation. As such,
Noon should mean the time when the sun reaches its highest elevation in the sky.
There are two things which make this an approximation. The first is the use of time zones. Here on the west coast of Wales, the sun sets fifteen minutes later than it does in London and similarly, noon - meaning the highest elevation of the sun - is fifteen minutes later as well. It used to be the case that every town operated to its own local time, but the coming of the railways made it necessary to keep the same time across the whole country. Imagine trying to devise a train timetable with a different time zone for each stop!
I can see the sense in having the same time across the country, so the time is accurate to within about half an hour. For that purpose we all use Greenwich time (the political choice of a location right at the east of the country is also a little irritating - somewhere in the middle would be better), but what about the
mean part of GMT? This is
mean in the sense of
average and derives from the fact that noon-to-noon is not exactly 24 hours, most of the time. On some days it takes a little more and on other days a little less than 24 hours for the sun to return to its highest elevation in the sky.
The reason for this variation is the eliptical shape of the Earth's orbit around the Sun. I was going to give you a brief explanation there, but then I looked it up and it got complicated. If you're interested, Wikepedia has a lengthy article on the subject. The upshot is that some of the time, a sundial is fast relative to a clock, and some of the time it is slow. When clocks were new, the sundial was taken to be correct and an adjustment was applied to the new-fangled clocks to calculate the correct, sundial time. Nowadays, if you are so inclined, you can apply the adjustment (in reverse) to sundial-time to get the
correct time as per a clock.
This leaves me in a quandry. I share the modern instinct that the regular clock, with exactly 24 hours each day, is the more correct measure of passing time, but if the sundial, which reliably reports the position of the sun, is inaccurate, what are we measuring with the clock? The concept
time of day has become abstracted away from the position of the sun, and that abstraction opens the door to people mucking around with it, with time zones and daylight saving. This feels wrong, as if we've somehow become separated from a fundamental aspect of the natural world. I am very tempted to set up a sundial in my garden and use only that for timekeeping. If only we had more sunlight.