|ΔT vs. time from 1657 to 1984
|Deviation of day length from international
standard second-based day, 1962–2010
|Aztec Calendar Stone
Graph showing the difference between
UT1 (succesor to GMT) and UTC
(Coordinated Universal Time). Vertical
segments correspond to leap seconds.
|Collier Smith - A Man with Time on His Hands
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|If you enjoy our quizzes, don't forget to order our books!
1. The Leap Second
2. To keep Universal Time the same as XXX
3. 30 Dec 2008
|Answer to Quiz #358
July 1, 2012
|1. What recent event?
2. Why did it happen?
3. When was the previous occasion this occurred?
|Comments from Our Readers
|It's nice to know that I'm not alone. The Earth and I are as one, we are both slowing
Very interesting. I have of course heard of leap days, but I don't think I ever knew they
did that kind of tinkering on the second level.
The last increase was Jan. 1, 2009.
If anyone gets this wrong, we'll give them a second chance.
- Q. Gen.
I'd do another puzzle in a New York minute.
BTW, the last addition of the Leap Second was Dec 31, 2008, delaying the start of
the New Year. We'll let it go this time....
- Q. Gen.
When I got the time listed correctly, I got San Francisco's webpage which mentioned
the leap second. Very timely quiz. Interesting that the leap seconds are necessary to
keep out time correct.
I did not change my wristwatch or any of the house clocks. My computer is run off of
the country's time signals and probably made the addition Sunday morning.
What did you do with all that extra time on Saturday? I tried to eat as much ice
cream as possible because I heard that whatever you consumed during the leap
second didn't have any calories.
- Q. Gen.
I did all that extra genealogy research while eating licorice in that extra time - those
calories don't count either.....
I'll bet you got an ice cream headache from eating that fast.
I've been indexing the 1940 census like crazy. Glad I stopped in for a peek at the
Too bad the Big Indexing Day was scheduled for July 1 and not June 30. Imagine
how many more records could have been indexed with all that extra time available.
People could have pooled their extra second and donated to a fund that could have
been used by a volunteer who otherwise would not have had time to participate.
- Q. Gen.
I would have had no idea except that the leap second managed to crash (or so they say)
the entire QANTAS booking system. That said, a post knowledge Google for '4:59:60'
+ time brought up leap second stories, so I guess I would have picked it anyway.
It was way back on 31 December 2008 that I was last able to enjoy that extra sleep due
to a leap second being added. Of course, since that was New Years Eve and I was
partying a bit, I wasn't sleeping anyway.
Time is on my side - Deus.
My leap second was spent relaxing! Making up for "lost" time. Ha ha ha.
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|I have a major advantage on this one: I worked as a public affairs specialist from 1969
to 2002 at the NIST Boulder Labs, where the atomic clock is housed, and wrote all the
press releases during that time concerning the introduction and implementation of "leap
seconds". I also edited books on this general subject, and wrote a number of pamphlets
on it, as well.
So, the answers are:
1. -- Leap second (probably the one on Saturday, 6/30/12, but it could have been
any of the 25 we have had).
2. -- Leap seconds are needed to make our modern time, which is kept by atomic
clocks and is very constant in rate, and astronomical time, which is based on the
spinning earth, in synch. Without adding (or subtracting) leap seconds from time to
time, the two kinds of time would gradually drift apart, and in the very long term
(thousands of years), we would find our clocks saying it was noon while the sun was
rising or setting. NIST's current clock system provides time so constant that it gains or
loses less than a second per 100 million years.
3. -- Leap seconds have been added 23 times since the first two in 1972.
Leap Seconds Inserted into the UTC Time Scale
(Always at 23:59:60 UTC -- the last second of the day, usually on Dec. 31 or
UTC is Universal Coordinated Time, the modern replacement for Greenwich Mean
Time for most of the world. Pacific Daylight Time is 7 hours earlier than UTC,
hence the leap second occurs at 4:59:60 pm PDT.
More info at:
It is in analogy to the extra day added during leap years to keep our calendars in step
with the seasons. Just as an extra "leap day" is added every 4 years (approximately), we
add an extra "leap second" in about 5 out of 8 years to keep our clocks in step with the
I won't bore you with all the other material on leap seconds, atomic clocks, and the
history of timekeeping in my files. But here is a brochure I co-wrote and revised many
times between 1970 and 1995 on the topic, and adapted to the Web:
In the 1840s a railway standard time for all of England, Scotland, and Wales evolved,
replacing several "local time" systems. The Royal Observatory in Greenwich began
transmitting time telegraphically in 1852 and by 1855 most of Britain used Greenwich
time. Greenwich Mean Time (GMT) subsequently evolved as an important and
well-recognized time reference for the world.
In 1830, the U.S. Navy established a depot, later to become the U.S. Naval Observatory
(USNO), with the initial responsibility to serve as a storage site for marine
chronometers and other navigation instruments and to "rate" (calibrate) the
chronometers to assure accuracy for their use in celestial navigation. For accurate
"rating," the depot had to make regular astronomical observations. It was not until
December of 1854 that the Secretary of the Navy officially designated this growing
|Yesterday, June 30 2012, a 'leap second' was added to clocks around
the world in order to account for the slowing of the Earth's rotation,
making the day one second longer than a normal Saturday. Although
the extra second went unnoticed by most, a few internet companies
had trouble dealing with unusual change to the atomic clocks.
Wired reports that web operators at Reddit, Mozilla and several other
internet companies experienced brief technical issues Saturday night,
when their software programs tripped up on the 'leap second' Wired
goes on to say that a lot of computing systems utilize the Network
Time Protocol to keep themselves lined up with the world's atomic
clocks. Last night, when a 'leap second' was added to the atomic
clocks, several computing systems weren�t sure how to respond.
At 6:41pm, Reddit confirmed via Twitter that they were having
technical issues due to the 'leap second'. 'We are having some
Java/Cassandra issues related to the leap second at 5pm PST. We're
working as quickly as we can to restore service,' Reddit Status
Reported by Jim Kiser
|New Year's Eve Ball
Times Square, NYC
|Peace Clock Tower
|Jens Olsen Clock
|Atomic Clock at NIST
|World Time Scales
|Did You Know That...
|Leap seconds can be positive (one second added) or negative
(one second omitted) - at least in theory: so far, all leap seconds
were positive, and given the slowing of the Earth's rotation it is
unlikely that a negative leap second will ever occur.
The speed of the Earth's rotation differs from day to day and
from year to year, so the difference between UT1 and TAI
varies accordingly. For example, the accumulated discrepancy
over one year was 0.28 seconds in 2011, but only 0.02 seconds
in 2001 (based on data from IERS).
Not only do days become longer, but the rate at which day
lengths increase also grows over time – but only by about two
thousandths of a second per century, according to Dr Bruce
Warrington, from Australia’s National Measurement Institute
(NMI). This means that at the moment days are 0.002 seconds
longer than the sum of 86,400 seconds measured by atomic
clocks; in 100 years, they are expected to be 0.004 seconds “too
Some scientists suggest abolishing leap seconds, effectively
redefining the way we measure time.
|Workarounds for leap second issues
Instead of inserting a leap second at the
end of the day, Google servers implement
a leap smear, extending seconds slightly
over a time window prior to the leap
|Ancient Sun Clock
|Types of Ancient Clocks
Read Collier Smith's NIST brochure.
Also click on links below each of
the following images.
|Ancient Persian waterclock and