Those who forget deserve to repeat history, or something like that. "Second-stretching" was already tried from 1960 to 1972. While one atomic clock kept TAI, another was "steered" to drift from it at a controlled rate to approximate UT2, and the "steering constant" was declared for six months or so at a time. That still wasn't perfect, and they declared mini-leaps of 50 or 100 ms. A total of 10 leap seconds were added in this manner before the present scheme was launched in 1972.
That scheme was considered too complex and unwieldy and the present scheme was viewed as an improvement in 1972. Anyone advocating a return to yesteryear should explain in detail while it will work better now. (it won't, enough said.) The other scheme I've seen proposed is leap-minutes or leap-hours. Those would obviously occur at about 1/60 or 1/3600 the random rate of leap seconds. That greater infrequency would lead to systems being LESS well designed to accomodate them in my opinion. IERS provides notification (Bulletin C) of the plan for a leap second with approximately 5 months advance notice of the actual leap second, which is always scheduled for the end of June or December. While longer intervals would be prefereable to "second stretching," I am convinced that those who fail to plan their systems for leapseconds would forget to plan for leapminutes. If earth rotation drifts further so that more than 1 leapsecond per year is required, the second choice is end of March and September, and third choice, the end of any month. Any system that is based on accurate time should either keep TAI or recognize that a leap second can be declared with advanced notice at the end of every month and operate a mechanism of obtaining that advance notice. I would note that most "atomic clock" products which receive radio time signals from WWB correctly decode and implemnent the leapsecond, and that NIST makes the notification available in their Internet time protocol as well (with less advanced notice). The GPS system keeps "GPS time" which is a fixed offset to TAI and broadcasts the differential leap second count in the navigational message. ________________________________ From: James Frysinger <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Thu, July 7, 2011 10:16:21 PM Subject: [USMA:50831] Stretching the second Folks, You might find this article of some interest. It reports an effort made by some people to convince the ITU (formerly, International Telegraph Union) to change the way that UTC is calculated, probably by departing from the "atomic second" as they call it -- actually, the unit second as defined by the SI. At least that's my reading of the article. Since all "leap seconds" have been positive, I suppose that amounts to them wanting to stretch the second, so to speak. Keep in mind, these are radio and TV folks, not metrologists most likely. My guess is that the ITU will listen politely and decline to take the recommended action. Jim http://www.foxnews.com/scitech/2011/07/07/scientists-fight-effort-to-redefine-time/?test=faces -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
