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Leap Second To Be Added Dec 31, 2008
ammorris writes "Don't be the laughingstock of your friends when you shout 'Happy New Years' a second too early ... The International Earth Rotation and Reference Systems Service has announced that a leap second will be added on December 31, 2008 at 23h 59m 60s, meaning that this year will be exactly one second longer. The last leap second occurred Dec 31, 2005; they are added due to fluctuations in the rotational speed of the earth. You can read all about leap seconds on Wikipedia."
Until 2007 legal time in the US was mean solar time, and that has no leaps, so this is the first leap second for the legal US time. Officially, of course, USNO and NIST were keeping UTC, but that didn't make it legal. The difference shows up in computer time scales.
Technically, the original announcement was in July. This is just a reminder.
The bulletin is dated 4 July 2008, it's just the Slashdot article that's late. Or even, just on time as a reminder.
The creatures outside looked from Alt-Right to Antifa; but already it was impossible to say which was which.
"Don't be the laughingstock of your friends when you shout 'Happy New Years' a second too early ... this year will be exactly one second longer."
So... wouldnt we be shouting it one second later than everyone else?
Yes, yes, that's Nix vs Hedden and it was ruling by the U.S. Supreme Court in 1893. The court ruled that in the common parlance of the time a tomato was seen to be a vegetable and not a "fruit of the vine", working from the assumption that most people at it for a main course instead of a dessert. I think that if you were going to pick up on the ridiculous nature of the case you'd focus on the reason behind the court case — that taxes needed to be paid on imported vegetables and yet not on imported fruit.
XML is like violence. If it doesn't solve the problem, use more.
Those of us in the U.S. will get to celebrate our extra second during a reasonable time of day, as it's in UTC. The local astronomy museum generally has a baloon drop at that time, so that the kids can feel they celebrated New Year's properly.
Bruce Perens.
Haven't they heard of NTP? http://en.wikipedia.org/wiki/Network_Time_Protocol
Yes, but we are talking about interfaces between a lot of different networks, each of which have their own GPS based time reference. An NTP daemon in each network talks to the GPS device, but there is no way to be sure that all the daemons will slew the time at the same rate.
http://michaelsmith.id.au
The length of the second doesn't change. An extra second is added. I work with precision timing systems where this is an issue.
The sequence is:
23:59:59 UTC
23:59:60 UTC
00:00:00 UTC
00:00:01 UTC
That means that the valid range for seconds is 0..60 and it is possible to have 61 seconds in a minute. You need to know this if you are using a programming language with range checks.
GPS uses its own time scale that isn't affected by leap seconds.
Mea navis aericumbens anguillis abundat
I'm sorry? Fluctuations in the rotation of the earth? You mean the earth is accelerating and breaking?
Yes, that's exactly what we mean (well, "braking" rather than "breaking"). The earth does not have a constant angular velocity. To conserve angular momentum, as the mass distribution of the earth changes (e.g. due to glacial rebound), the spinning of the earth speeds up and slows down. It also slows down a little due to tidal braking. So a "day", as measured by the rotation of the earth relative to the fixed stars, is not exactly 86400 seconds. It's generally a little more, around 86400.001 seconds at present, and it varies from day to day and from year to year. Now that civil time (UTC) is kept with atomic clocks, this is a genuine problem. Leap seconds are introduced to keep UTC close to UT1 (astronomical time).
It has nothing to do with the fact that a rotation around the sun is not exactly 365.25 rotations around our own axis? hmm...
That's right. Leap seconds have nothing whatsoever to do with that. They don't affect the calendar. That's what leap days are for. Leap days keep the calendar in sync with the seasons (by setting the average calendar year length to 365.2425 days, very close to the vernal equinox year which is currently 365.242374 days).
Yes, the GPS system uses its own internal GPS time which is different from UTC. But the difference is always exactly an integer number of seconds and the GPS system is made aware of the changes to this difference (like when a leap second is added) so a GPS unit can and should display UTC correctly, ie 59, 60, 00.
It has nothing to do with the fact that a rotation around the sun is not exactly 365.25 rotations around our own axis?
No, it does not. Leap days are about keeping the calendar in sync with the seasons. Leap seconds are about keeping the clock in sync with the rotation of the earth. These are two different components of motion, and they are handled with different measures.
Then switch to a stable time scale: http://en.wikipedia.org/wiki/International_Atomic_Time
The UTC second 60 gets added at midnight only at those locations where UTC == local time, i.e. places like England.
For us in the rest of Europe, the leap second will be added an hour after local midnight, i.e. at 01:00:60 CET.
Terje
"almost all programming can be viewed as an exercise in caching"
Leap years are a separate issue. They keep the calendar in sync with the seasons. Leap seconds keep our clocks in sync with the apparent positions of the Sun and stars.
Mea navis aericumbens anguillis abundat
Why are you drawing attention to it? Just let the moderation system do its job. It only takes one mod to drop an AC into -1 oblivion.
http://michaelsmith.id.au
The redistribution of mass after the 2004 Indian Ocean undersea earthquake was enough to measurably affect the rate of the Earth's rotation; the Three Gorges Dam project will also have a minute effect due to the concentration of water in the reservoir that's formed.
Leap days and leap seconds serve different purposes.
Leap days are because our definition of a day (and thus a year) are not exact. A year is actually ~365.25 days, so we add an extra day every 4 years to compensate.
Leap seconds are needed as there's another small random variance in the length of a day (The mean solar day lengthens by about 1.7ms per century, due to slowing of the earth's rotation), so we occasionally need to add a second to keep us in sync with astronomical time.
upon the advice of my lawyer, i have no sig at this time
"Slew the time"? What system does that? According to the following page, the NTP server announces the leap second in advanced, and "well-behaved" kernels count the extra second like they are supposed to; i.e. there is no slewing:
http://www.cis.udel.edu/~mills/leap.html
I hold it, that a little rebellion, now and then, is a good thing. -- Thomas Jefferson
There is a drift, and there are fluctuations.
Regarding the drift: The day length is getting gradually longer by about 1.7 milliseconds every century (+2.3ms due to tidal braking, -0.6ms due to glacial rebound). In about 1820 the day was 86400 seconds; now it is longer than that. In a thousand years, the day will be about 86400.017 seconds, and we will need a leap second every couple of months.
[Note: I am simplifying a little here for the sake of clarity by ignoring the difference between a solar day and the stellar and sidereal days, which are about 4 minutes shorter].
Regarding the fluctuations: There are fluctuations of the earth's angular velocity on many timescales. It fluctuates with weather, with the seasons, and with major events on the surface (e.g. a dam creating a new reservoir) and in the earth's crust (e.g. an earthquake or major volcanic eruption) and deeper interior (e.g. we don't really know). All these events are minor rearrangements of the mass of the earth, which change its moment of inertia. Conservation of angular momentum dictates that the angular velocity must change, and it does. Of course the earth isn't a rigid body and that complicates all this. Learn about Geodesy if you want to know more.
In the 1990s the day length was approximately 86400.003 seconds, so we needed a leap second every year. For poorly-understood reasons (possibly some sort of deep mantle activity), the earth's rotation speeded up around the year 2000, and for a while the day length was about 86400.0004 seconds. Now it is slower again, about 86400.001 seconds. These changes all come under the "fluctuations" heading.
There is an organisation called the IERS - International Earth Rotation and reference Systems Service - which collects measurements of all this stuff to very high accuracy and produces all sorts of reports, bulletins, data sets, etc etc.
No it isn't. It's a 86401 seconds longer. Than last year. Or 86400 longer than the previous leap-second-year 2005. Oh, yeah, it's exactly 1 second longer than 2004 and 1996.
I confess enjoying myself as a time nazi. Should not forget to count february 29th...
The NTP daemon is normally used to interface with GPS clocks and to distribute time around a LAN. It never allows time to just jump. It always slews the clock.
This, of course, is wrong.
First, by default it steps the time on startup, with a default limit of 1000 seconds offset, but you can disable this limit.
Second, after startup, by default it slews the time unless the offset is greater than 128ms, in which case it steps the time. The 128ms value is configurable via the "tinker" command, but it is not recommended that it be changed.
See here under 'What's the problem?'
Um, no, that is not true. Unix time is kept in non-leap seconds elapsed since a defined point in time. Look it up.
Are you adequate?