Standard Time now — Page 402, Lesson 356

I want to walk you through Standard Time now. We've already dealt with Local Mean Time and Zone Time, so let's see why neither of those works for a country on land, and what we do instead. Zone Time, remember, is that system of 15-degree-wide bands that gives ships at sea a convenient standard, keeping the hours of the day roughly in step with daylight and darkness. But that system would be completely inappropriate on land. Here's the classic example: the 7.5°E longitude line runs right through the middle of Nigeria. If Nigeria used Zone Time, western Nigeria would be on one zone and eastern Nigeria on another — it would be inconvenient, to say the least, if western Nigeria kept a time 1 hour in advance of eastern Nigeria. One country, two different times. That's the problem. Now, Local Mean Time is equally inappropriate as a national standard. Think about the UK. At 1200 LMT in Greenwich, the time at Oxford, which is at 001°20′W, would be 1155 LMT. And the time in Penzance, at 005°W, would be 1140 LMT. So within one small country you'd have a spread of 20 minutes between Greenwich and Penzance. And that situation actually did exist in the UK up until the mid-1800s, when lines of communication were slow. Nobody cared much because nobody travelled fast enough to notice. Then came the railway system. With the advent of the railways, the need for a standardized system was recognized. And here's a lovely piece of history: in those very early days, train guards leaving London carried a watch set to Greenwich time. At each station out of London, the station clock would be reset to the guard's watch — that is, to GMT. And then, subsequently, church wardens would set the church clocks to the station clock, i.e. to London time. So each town in the UK set its clocks to a standard time for the whole country. That was the foundation of the Standard Time system — the ST system. So what is Standard Time? Each country nominates its own Standard Time, and it's normally notified in the Air Almanac as a correction to UTC. Clearly, each country aims to fix its Standard Time such that 1200 hr ST occurs about the middle of the period of light, and 0000 hr ST occurs about the middle of the period of darkness. In other words, noon by Standard Time should be roughly when the sun is highest, and midnight roughly in the middle of the night. That means Standard Time will be close to both Local Mean Time and to Zone Time — but it will not be exactly the same as either. It's a compromise chosen for convenience. Now, for the UK specifically: the Standard Time is UTC — which is the same as GMT — at all times of the year. In summer, we adjust our clocks forward 1 hour and refer to the time as British Summer Time, BST, which is simply one hour added on to our Standard Time, UTC. Summer Time and Daylight Saving Time corrections are discussed later in these notes, so we'll come back to that. For your navigation work, the practical point is this: Standard Time corrections for most countries are listed in the Air Almanac on pages 1 to 4 inclusive. The countries are listed in three general areas. List 1 is on pages 1 and 2. And that's where we'll pick up next — the structure of those lists.