[LEAPSECS] What's the point?

Ian Batten igb at batten.eu.org
Thu Feb 10 08:56:22 EST 2011

On 10 Feb 11, at 0122, Mark Calabretta wrote:


> On Wed 2011/02/09 11:44:14 PDT, Warner Losh wrote

> in a message to: leapsecs at leapsecond.com


>> The speculation on the list is that in the absence of a central

>> authority, local governments will act as their people request when it is

>> staying dark too late and parents can't get their kids to bed with the

>> sun still shining, or have to drive to work in the dark too many days of

>> the year.


> Yes, it seems a likely response. The underlying assumption is

> that people expect the Sun to be roughly overhead at noon to

> within a tolerance of about an hour.

I don't think that's quite true. For a start off, in large parts of the world "overhead" simply means "at its zenith" which might be quite low in the sky, and to determine where it's "solar" 1100, 1200 or 1300 would require careful observation. So peoples' sensitivity is probably a lot coarser than you imply.

And people routinely live in places where solar time is several hours adrift from civil time --- Brest, France for example is four degrees west of Greenwich, yet in the summer is on UTC+2 --- so at noon civil time it is 0945 solar time. The pressure to move the UK onto "European" (ie UTC+1/UTC+2 daylight saving) mostly comes from the south of England, which would leave Cornwall in a similar position to Brest: there's a lot of enthusiasm for it, as long, light evenings are great for the tourist industry. I suspect people in 2011 are more tolerant of that scenario than they would be of the opposite, where at 1200 solar it's 0945 civil, leading to very dark evenings. So I think the limits for social acceptability on civil/solar offsets are asymmetric, with three hours on way probably acceptable in some situations, while one hour the other may cause some dissent.


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