[LEAPSECS] Straw men

Ian Batten igb at batten.eu.org
Mon Jan 9 17:43:31 EST 2012

On 9 Jan 2012, at 2129, Rob Seaman wrote:


>> Pages 7 and 8 appear to be assertions that it's true, rather than any solid reasons why it's true.


> I'll try harder next time.

The problem is

> A more accurate statement is: “Civil time is mean solar time”, because this is really just a definition of terms (p.7)

I know you really, fervently believe that to be not only true currently but inevitably and essentially true, but it just isn't. For a start off, as the examples of Penzance, Vigo and Brest show (and I'm sure there are other examples of places 4 and more degrees east of the timezone they are administratively placed in where the offset is in the opposite direction), civil time is at best a very loose approximation of mean solar time as adjusted for the local timezone. Civil time _used_ to be closer to mean solar time, but the coming of the railways and the development of large extra-national organisations has rather stopped all that. When civil time is routinely an hour or more out from local mean solar time, the issue of TAI, UTC, UT1, etc is in the noise floor, and will remain so for hundreds of years to come.

DST massively complicates matters, so that for an hour a year civil time is discontinuous and for another hour it's not only discontinuous but also not even monotonic. But let's ignore that, and consider the case of local civil time in November: its relationship with mean solar time is loose in the extreme, and changes as you drive up the A30, the M5 and the M4 from Penzance towards London, or insert your own eastbound journey. By driving for four hours, you can alter the relationship between civil time and mean solar time by twenty minutes. If it's a requirement that civil time be mean solar time, then the fact that a four hour drive has the same effect as several centuries of drift is a bit of a contradiction.

And I think this is at the heart of your failure to convince people. I think civil time is a distant relative of mean solar time, which in order to reflect some long-standing cultural assumptions is maintained as something approximately aligned to mean solar time. However, as tradition and convenience diverge, people who need to know the difference know where to get it and for everyone else, it just doesn't matter. Timetables, appointments and the TV Guide are in civil time; your watch is set to civil time; your computer and your PCR display civil time; the radio news bulletin announces civil time. If the sun's directly overhead at 9pm you might get concerned, but so long as it's not as absurd as that, you don't care, just so long as the ten o'clock news starts at ten o'clock, whether you're in London or Penzance (this argument applies, mutatis mutandis, in countries with multiple time zones)

Now there are use-cases, of which you have many, which mean you need access to assorted high-precision time scales with defined properties (I assume most of them are about earth orientation, and therefore intimately tied up with your physical location). At the moment, you can derive those to high precision from UTC, DUT1, your location and some other constants. Were UTC not to be hitched to UT1, either DUT1 will become larger in magnitude (which you foresee presenting problems), or an extra variable representing the integer portion of DUT1 (which will obviously change more slowly, having a resolution of only 1s, but will change over the lifetime of a given system) needs to be distributed somehow, or you're screwed. We understand that. There's also some merit --- but, as I suspect you deduce from the vibes, a merit not everyone is convinced of --- in the idea that the status quo is changing and therefore those the onus is on those that wish to see the change.

But the argument that there is an inherent need for civil time to be coupled to mean solar time is debatable, to put it mildly, and your continued assertion that it's necessarily true and there's no point in debating it is putting people off the rest of your argument. You either need to justify it a lot more carefully, including explaining why the ~2 hour offsets routinely seen today don't cause anyone any difficulty, and why in some countries (ie, the UK) there are serious proposals with popular support to _increase_ the offset, or you need to construct the rest of your argument without reference to this not-axiom. Because at the moment, people can immediately see that the claim is untrue in many cases, and therefore that any argument built on it is similarly untrue.


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