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	Leap second - Wikipedia, the free encyclopedia
		Leap seconds are used to keep time standards synchronized with civil calendars, the basis of which is astronomical.
		The SI second that is counted by atomic time standards has been defined in such a way that its length matched the nominal second of 1/86400 of a mean solar day between 1750 and 1892.
		Leap seconds occur only at the end of a UTC month, and have only ever been inserted at the end of June 30 or December 31.
	en.wikipedia.org /wiki/Leap_second (1950 words)

	Talk:Leap second - Wikipedia, the free encyclopedia
		I think you'll probly find that there's two seconds: One of which is 1/246060 of a day long, and one of which is precisely "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom", whatever that means.
		When UTC was established in 1972, harmonizing the definition of the civil second and the atomic second, we chose to adjust for the inevitable differences between the rock-solid UTC and the highly variable UT1 (earth rotation time) in one-second jumps.
		Leap seconds are announced six months in advance, and occur simultaneously around the world during the last minute of June or December, at 23:59:60 UTC.
	en.wikipedia.org /wiki/Talk:Leap_second (4909 words)

	The NTP Timescale and Leap Seconds
		Leap seconds were inserted prior to 1 January 2006 on the occasions listed in the leapseconds file, a current copy of which can be obtained from NIST or via the NTP Autokey security protocol.
		The intervals between leap insertions has been increasing; the interval since the next scheduled leap second at the end of 2005 and the last one at the end of 1998 was seven years.
		Thus, all previous leap seconds, not to mention the apparent origin of the timescale itself, lurch backward one second as each new timescale is established.
	www.eecis.udel.edu /~mills/leap.html (1423 words)

	NIST Time and Frequency FAQ (Site not responding. Last check: 2007-11-05)
		Leap years are necessary because the actual length of a year is 365.242 days, not 365 days, as commonly stated.
		Leap seconds are needed so that users of the astronomical time scale (UT1) can use UTC and know that the difference between the two time scales is never greater than 0.9 seconds.
		When a leap second is necessary, an announcement is made at least several months in advance, and all leap seconds so far have been implemented on either June 30th or December 31st.
	tf.nist.gov /timefreq/general/leaps.htm (497 words)

	Leap seconds
		It is also possible to have a negative leap second, where one second is removed, in a case where the Earth is rotating faster, but such a negative second has never been used, and is rather unlikely to be used in the future.
		Leap seconds are inserted at the end of June or December as an additional second after 23:59:59 UTC (Universal Time Coordinated).
		The additional second is the 61st second of the last minute of the month, and it is written as 23:59:60 (or 11:59:60 PM in 12-hour format).
	www.timeanddate.com /time/leapseconds.html (842 words)

	BBC NEWS \| Science/Nature \| New Year 'delayed' by leap second
		Leap seconds are required every so often to keep our clocks in sync with solar time used by astronomers.
		A leap second is added to Co-ordinated Universal Time (UTC) to keep it in step with solar time - based on the Earth's rotation on itself - to within a second.
		The new leap second will be inserted at the end of the final minute of 2005, giving the familiar "six pip" BBC radio time signal an extra pip before the long pip marking the hour.
	news.bbc.co.uk /1/hi/sci/tech/4562194.stm (286 words)

	USNO Leap Second Press Release (Site not responding. Last check: 2007-11-05)
		On December 31, 1998 a leap second will be added to the world's clocks at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC), corresponding to 6:59:59 pm Eastern Standard Time.
		Since 1972, leap seconds have been added at intervals varying from six months to two-and-one-half years - this leap second is eighteen months since the last one.
		Leap seconds are added because the Earth's rotation is tending to slow down.
	www.usno.navy.mil /leap98rel.html (767 words)

	Leap second in UTC (Site not responding. Last check: 2007-11-05)
		Since the adoption of this system in 1972, firstly due to the initial choice of the value of the second (1/86400 mean solar day of the year 1820) and secondly to the general slowing down of the Earth's rotation, it has been necessary to add 21 s to UTC.
		The decision to introduce a leap second in UTC is the responsibility of the International Earth Rotation Service (IERS).
		The leap second is announced in Bulletin C.
	hpiers.obspm.fr /eop-pc/earthor/utc/leapsecond.html (316 words)

	USATODAY.com - 2006 will be delayed by a 'leap second' (Site not responding. Last check: 2007-11-05)
		A leap second will be inserted in the world's clocks just before midnight — Greenwich mean time —; on New Year's Eve, the U.S. Naval Observatory reported Friday.
		Leap seconds are needed occasionally because modern atomic clocks measure time with great accuracy, while the rotation of the Earth can be inconsistent.
		This will be the 23rd leap second that has been inserted since 1972 when an international timekeeping agreement was signed, according to the Observatory.
	www.usatoday.com /tech/news/2005-12-25-leap-second_x.htm (192 words)

	NIST Time Scale Data Archive (Site not responding. Last check: 2007-11-05)
		The first leap second was inserted into the UTC time scale on June 30, 1972.
		Leap seconds are used to keep the difference between UT1 and UTC to within ±0.9 s.
		All leap seconds listed in the table are positive leap seconds, which means an extra second is inserted into the UTC time scale.
	tf.nist.gov /pubs/bulletin/leapsecond.htm (354 words)

	New Year’s Day 2006 delayed by a second - U.S. Life - MSNBC.com (Site not responding. Last check: 2007-11-05)
		Scientists are delaying the start of 2006 by the first “leap second” in seven years, a timing tweak meant to make up for changes in the Earth’s rotation.
		The first leap second was added on June 30, 1972, according to NIST, an arm of the U.S. Commerce Department.
		Although it is possible to have a negative leap second --that is, a second deducted from Coordinated Universal Time --so far all have been add-ons, reflecting the Earth’s general slowing trend due to tidal braking.
	www.msnbc.msn.com /id/10605881 (392 words)

	Leap seconds (Site not responding. Last check: 2007-11-05)
		Leap seconds were introduced in 1971 to reconcile astronomical time, which is based on the rotation on the Earth, and physical time, which can be measured with amazing accuracy using atomic clocks.
		Leap seconds have to be inserted on average every 1–2 years during this century.
		Abandoning leap seconds in the international standard time would not cause any problems for computer systems that are not involved in controlling astronomical or aerospace systems, as long as national/regional civilian time zones do the same.
	www.cl.cam.ac.uk /~mgk25/time/leap (2123 words)

	ipedia.com: Leap second Article (Site not responding. Last check: 2007-11-05)
		Leap seconds can occur only at the end of a month, and have only ever occurred at the end of a 30 June or 31 December.
		Unlike leap days, they occur simultaneously worldwide; for example, a leap second on 31 December will be observed as 7:59:60 pm U.S. Eastern Standard Time.
		Between January 1970 and November 2001, the IERS gave instructions to insert a leap second on 22 occasions.
	www.ipedia.com /leap_second.html (428 words)

	Geek.com Geek News - One leap second to be added to 2005 (Site not responding. Last check: 2007-11-05)
		The first leap second was added on June 30, 1972, and the last one was added in 1999.
		One arc second of orbit of the planets Jupiter or Pluto is a very large distance travelled and a crucial measure to be made when sending expensive space craft to snoop around the surfaces of those planets.
		The leap second will be added just before 00:00 UTC between 2005 and 2006, so if you don't live in that timezone it will affect you at some other time during the day, for example just before 7 PM (12/31) in New York (Source).
	www.geek.com /news/geeknews/2005Dec/gee20051226033965.htm (2016 words)

	Future of Leap Seconds
		Note that the effective date of the end of leap seconds proposed by the 2004 contribution of the United States is 2007-12-21 which is less than two months after the conference.
		Finally, as a result of the invention of leap seconds, systems designers and the general public have not had to recognize that time-of-day (universal time) and time interval (atomic time) are two distinct and incommensurate quantities.
		Given that UTC with leap seconds originated in 1972, and that atomic time did not exist before 1955, it is not clear that any meaning dare be attributed to the fractional bits of the NTP clock during most of the first half of the present NTP era.
	www.ucolick.org /~sla/leapsecs/onlinebib.html (12489 words)

	NIST Tech Beat - Dec. 21, 2005
		This year's leap second will be implemented by adding an extra second to atomic clocks at NIST in Boulder, Colo., and other sites around the world.
		Normally, the last second of the year would be 23:59:59 UTC on Dec. 31, 2005, while the first second of the new year would be 00:00:00 UTC on Jan. 1, 2006.
		A recent proposal to eliminate leap seconds altogether in the future is still under consideration by the international bodies in charge of coordinating world time.
	www.nist.gov /public_affairs/techbeat/tb2005_1222.htm (1986 words)

	BBC NEWS \| Science/Nature \| Leap second talks are postponed
		Leap seconds synchronise clock time with solar time used by astronomers.
		The first leap second in seven years will be added at the end of 2005.
		Daniel Gambis, of the Earth Rotation Service in Paris, which decides when to add or subtract leap seconds, told the BBC: "For me, it would be a problem if the Sun were to rise at 4pm or at a different time like noon or midnight.
	news.bbc.co.uk /1/hi/sci/tech/4420084.stm (543 words)

	Leap Seconds
		Thus, the definition of the ephemeris second embodied in Newcomb's motion of the Sun was implicitly equal to the average mean solar second over the eighteenth and nineteenth centuries.
		Over the course of one year, the difference accumulates to almost one second, which is compensated by the insertion of a leap second into the scale of UTC with a current regularity of a little less than once per year.
		Since the first leap second in 1972, all leap seconds have been positive and there were 23 leap seconds in the 34 years to January, 2006.
	tycho.usno.navy.mil /leapsec.html (1741 words)

	2006 Postponed by One (Leap) Second (Site not responding. Last check: 2007-11-05)
		The planet's slowing is mostly due to the friction of tides raised by the gravitational pull of the sun and the moon.
		The most recent leap second was added seven years ago, in 1998.
		As the Earth slows, the addition of leap seconds will be required more frequently to keep the Earth and atomic clocks in sync.
	news.nationalgeographic.com /news/2005/12/1229_051229_leap_second.html (558 words)

	U.S. Naval Observatory to Add Leap Second to Clocks \| SpaceRef - Your Space Reference
		This marks the 23rd leap second to be added to UTC, a uniform time-scale kept by atomic clocks around the world.
		This leap second is occuring seven years since the last one.
		Leap seconds are added because the Earth's rotation tends to slow down relative to atomic time.
	www.spaceref.com /news/viewpr.html?pid=18607 (929 words)

	'Leap second' to be added on Dec. 31 \| News.blog \| CNET News.com
		The adjustment, called a leap second, takes place whenever Coordinated Universal Time is out of synch with the planet's time by more than 0.9 seconds.
		The last time a leap second was added was 1998, but usually they're added slightly less than once each year, NIST said.
		The first leap second was added in 1972, and often the extra second has been added at the end of June instead of the end of December.
	news.com.com /2061-11204_3-6009898.html (331 words)

	Why the US wants to end link between time and sun (Site not responding. Last check: 2007-11-05)
		But adding these ad hoc "leap seconds" -- the last one was tacked on in 1998 -- can be a big hassle for computers operating with software programs that never allowed for a 61-second minute, leading to glitches when the extra second passes.
		Eliminating leap seconds will make sextants and sundials slowly become inaccurate, but supporters say that's OK now that the satellite-supported GPS can give exact longitude and latitude bearings to anyone with a receiver.
		The U.S. effort to abolish leap seconds is also firmly opposed by Britain, which would further lose status as the center of time.
	www.post-gazette.com /pg/05210/545823.stm (1220 words)

	jwz - Happy Leap Second
		This decision is widely complained about to this day, but its also somewhat understandable — it'd be somewhat gross to require libc have access to an up-to-date list of leap seconds just to handle localtime() Therefore the kernel's idea of time_t must be set after each leap second event.
		However, the leap second was corrected by NTP during the daily run.
		p-second.htm seems to confirm that: "If an NTP daemon detects a leap second announcement, it passes the announcement on to its clients, and notifies its own operating system clock of the upcoming leap second, if the operating system is aware of leap seconds.".
	jwz.livejournal.com /585295.html (798 words)

	The Why Files \| Leapin' leap second
		But in 1972, after the invention of the hyper-accurate atomic clock, timekeepers began slipping in a leap second every few years, so atomic-clock time would jibe with time derived from Earth's position in space.
		Throwing the leap second to the sharks, they say, will make it easier to develop and maintain global positioning satellites (GPS) and computer communications.
		They say people who operate GPS and other time-critical gadgets have trouble accounting for leap seconds, which are somewhat unpredictable and thus tough to factor into software.
	whyfiles.org /shorties/187timeout (968 words)

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