Path: csiph.com!weretis.net!feeder6.news.weretis.net!news.alt.net From: "James Wilkinson Sword" Newsgroups: alt.comp.hardware.pc-homebuilt,comp.lang.c,comp.lang.ada,comp.programming,alt.comp.os.windows-10,alt.os.linux.ubuntu Subject: Re: 'Leap Second' to Be Added on New Year's Eve This Year Date: Thu, 05 Jan 2017 21:41:40 -0000 Organization: ~ Lines: 65 Message-ID: References: <5f5afd36-1ba2-f4e2-62ef-57a652f3170c@verizon.net> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15; format=flowed; delsp=yes Content-Transfer-Encoding: 7bit User-Agent: Opera Mail/1.0 (Win32) Xref: csiph.com alt.comp.hardware.pc-homebuilt:35521 comp.lang.c:101205 comp.lang.ada:32716 comp.programming:7268 alt.comp.os.windows-10:32675 alt.os.linux.ubuntu:194683 On Thu, 05 Jan 2017 19:28:59 -0000, wrote: > In comp.lang.ada James R. Kuyper wrote: >> On 12/31/2016 04:57 PM, James Wilkinson Sword wrote: >> > On Thu, 22 Dec 2016 13:43:58 -0000, Mr. Man-wai Chang wrote: >> ... >> >> A "leap second" will be added to the world's official clocks on Dec. 31 >> >> at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC), >> >> which corresponds to 6:59:59 p.m. EST; the clocks will read 23:59:60 >> >> before ticking over to midnight. The goal is to keep two different >> >> timescales in sync with each other. >> >> >> >> The units of time had long been defined based on Earth's rotation >> >> relative to distant celestial bodies. But that changed with the >> >> invention of atomic clocks in the mid-20th century; scientists then >> >> decided to base the second on the natural vibrations of the cesium atom. >> >> [How to Build the Most Accurate Atomic Clocks (Video)] >> >> >> >> These two timescales don't match up exactly, however. Measurements show >> >> that, because the moon's gravitational pull and other factors are >> >> gradually slowing Earth's spin, the rotation-based scale loses between >> >> 1.5 and 2 milliseconds per day compared to atomic time ? meaning the two >> >> diverge by a full second every 500 to 750 days. >> >> >> >> Leap seconds are a way to make up for this difference. Since 1972, the >> >> International Earth Rotation and Reference Systems Service (IERS) ? the >> >> That name always struck me as rather funny - it seems to imply that >> they're responsible for making the Earth rotate. What they're actually >> responsible for is keeping track of the Earth's rotation. >> >> >> organization that keeps track of time for the world ? has added 26 leap >> >> seconds to atomic clocks, with the last such insertion coming on June >> >> 30, 2015. >> >> >> >> The aim is to keep the two timescales within 0.9 seconds of each other. >> ... >> > I wish they'd turn their attentions to not turning the clocks back and forth all the fucking time! >> >> If you could make the Earth rotate at a fixed rate, there would be no >> need for leap seconds. It's perfect feasible, though the costs would be >> astronomical. Would you care to pay enough in taxes to make that happen? > > Changing _time_ is a nonsense and Earth rotation has little to > do with this: > > - most of ordinary time use is conventional and shift of few minutes > will not chage much. AFAICS to accumulate 5 minutes difference > we need hundreds of years, plenty of time to update conventions > if needed. In precision use jumping time is bigger hurdle than > help: astonomers care about differences much smaller than a > second. > - if one really wants to follow Earth rotation time base still > should be continous and at most mapping from "universal" to > "local" time should change. Given that basic time unit is > second we probably should designate one specific moment as > start of rational era and simply measure time in second > relative to this moment. UTC could be reasonable approximation > to rational time, but leap seconds spoil its properties. +1 -- Money can't buy you true love. It does however put you in a good bargaining position.