The Leap Second: a Jump in Time

Did you know? Leap seconds are adjustments made to Coordinated Universal Time (UTC) so that the UTC time standard, which is measured by atomic clocks and used for international timekeeping, can be synchronized with astronomical time to within 0.9 seconds.

The Earth’s rate of rotation around its axis is irregular, while atomic clocks are engineered to tick at the same speed for eons. The addition of leap seconds ensures astronomical time and UTC (otherwise known as Greenwich Mean Time) remain in accord.

earth rotation

The standard allows leap seconds to be applied at the end of any month, but so far all have been implemented on June 30 or December 31. Since their adoption in 1972, 25 leap seconds have been inserted, the last of which took place on June 30, 2012 at 23:59:60 UTC. The next one is scheduled for June 30, 2015 at the same time.

What’s in a Second?

The average day has 86,400 seconds, but atomic clocks do not define one second as 1/86,400 of the time it takes the Earth to travel around its axis. In atomic terms, one second is 9,192, 631,770 cycles of the standard Cesium-133 transition.

It’s an intricate calculation that’s incredibly precise, whereas the Earth’s rotation is slowing down over time, making the days irregular in length. An Earth day averages 0.002 seconds longer than the time tabulated by the atomic clocks. The result is a discrepancy of about one second every year and a half. Leap seconds ensure this discrepancy does not get too vast over time.

In theory, at least, leap seconds can be positive (with one second added) or negative (one second omitted), depending on the status of astronomical time results. All leap seconds have been positive so far, and the current pace of the Earth’s rotation makes it unlikely that a negative one will ever come into effect.

The Future of Leap Seconds

Some scientists want to abolish leap seconds, which would effectively redefine the way time is measured, but a consensus has yet to be reached on the subject. In 2012, attendees at the World Radiocommunication Assembly in Geneva scheduled a new vote on the matter for 2015.

Arguments against leap seconds include the following:

  • They are an anomaly, making them a cause for concern with safety-oriented real-time systems, such as air-traffic control programs that use satellite navigation.
  • Leap seconds are potential disruptions in computer systems that are closely synchronized with UTC.

2012’s leap second played havoc with LinkedIn, Reddit, Yelp, and other sites and applications. The Qantas Airlines computer system even went down for hours, forcing staff to check in passengers manually.

Coding for these apps and systems are based on UNIX, which appeared in 1970, before leap seconds came into effect. When the International Earth Rotation and Reference Systems Service, which maintains global time, signals to these computers that a certain minute has 61 seconds, Unix-based software systems become unstable.

Google developed a solution after the leap second of 2005 caused system issues. It slowly adds a couple of milliseconds to the clocks on its servers throughout the day of an impending leap second, which bypasses the security settings without triggering disaster.


Google’s fix has not been universally applied, and opponents of the leap second remain insistent that any time calibration benefits are overshadowed by the technological crises they cause. They point out that even if a leap second were applied every year, astronomical time would only be 16 minutes behind atomic schedule by 3015.

A Clockwork Strontium: The Future of Timekeeping

In early 2014, a new atomic clock was unveiled at JILA, a joint institute of the University of Colorado Boulder and the National Institute of Standards and Technology (NIST). This strontium atomic device, which set new world records for both stability and precision, has been heralded as a breakthrough in the science of timekeeping.

Atomic clocks keep time based on the frequencies of atoms. Their performance is measured by two primary metrics. The first is stability, or the variation of its speed. The second is precision, which is how closely the clock reaches the frequency at which its atoms oscillate between two energy levels.

First Atomic ClockThe first atomic clock was invented in 1949 at NIST (then known as the National Bureau of Standards) and, because of its accuracy compared to other timekeeping technologies, a new field of research evolved. Photo Credit: NIST.

According to NIST representatives, this clock is so precise that it can keep perfect time for 5 billion years. A small interior chamber contains strontium atoms suspended in a crisscross of laser beams.

When researchers ping them, they vibrate at lightning-quick frequency, turning the clock into a type of atomic metronome ticking out the seconds in tiny fractions.

Record Holder

It is the first clock to hold world records for both stability and precision since cesium fountain atomic clocks became available in the 1990s, and is around 50 percent more accurate than the previous record holder, which is NIST’s quantum clock. Because of its high performance level, it presently serves as the time and frequency standard for the United States.

Thomas O’Brian, who heads NIST’s Time and Frequency Division, said that the clock’s unprecedented ability will “not only lead to better use of things like GPS, but probably open up entirely new applications that I’m not even smart enough to think of yet.”

Technology That Underscores the Atomic Clock

Perfect timekeeping is essential for maintaining a lot of modern tools and conveniences, such as GPS, global telecommunications, and electrical grids. The technology that underscores the strontium atomic clock is so sensitive to gravity, magnetic fields, force, motion, electrical fields, temperature, and other phenomena that it could potentially be used to map the earth’s interior, or help locate underground water springs and other subterranean resources. If a network of these clocks were positioned in space, they could conceivably detect the gravitational waves generated by exploding stars and black holes.

JILA/NIST Fellow Jun Ye and the strontium lattice clock. credit: J. Burrus/NIST

The Next Time Standard?

National Institute of Standards and Technology scientists continue to develop next-generation atomic clocks using different atoms as a base: mercury, ytterbium, aluminum, and calcium. Although still in the experimental stage, these clocks have been showing rapid progress in their timekeeping ability, and each atom type has its own distinct advantages. At the very least, they may enable new technologies, and one might become the next time standard.

Top 5 Atomic Products for Daylight Saving Time

If you’re tired of resetting your clocks and watches for Daylight Saving Time (DST) twice a year, then turn to Atomic timekeeping! Atomic timepieces receive a radio signal twice a day from the National Institute of Time & Technology, making them accurate to 1 billionth of a second.

Check out our top 5 Atomic picks for DST this year:

(1) La Crosse Technology WT-3126B 12″ Atomic Analog Wall Clock

87111Customer Favorite! Enjoy the convenience of never having to set your clock again with this 12″ Atomic analog wall clock by La Crosse Technology. Special features of this atomic wall clock include accurate timekeeping, 4 time zone settings, a durable stainless steel case, auto-updates for DST, and simple operation.

View details:

(2) Quartex® Atomic Clock Movement

14352Our popular Quartex® Atomic clock movement auto-synchronizes with official U.S. time up to 5 times per day. These atomic clock movements are the most accurate clock movements on the market today. Bonus: A free pair of hour and minute hands are included with each movement!

Use in your next project:

(3) Men’s Atomix® Atomic Solar Watch

87177Our men’s Atomix® Atomic solar watch offers the precise timekeeping and style on a stainless steel band. The gunmetal-colored dial features large Arabic numbers and a smaller circle that shows 24-hour military time. Never reset the time on your watch again! Makes a great gift item.

See specifications:

(4) La Crosse Technology WT-5220U-IT Atomic Projection Alarm Clock

87214Never be late again with this projection alarm clock from La Crosse Technology! This alarm clock displays the time and temperature on the ceiling or wall in easy-to-read numbers. Features Atomic timekeeping that auto-updates for DST twice a year.

Best seller! View now:

(5) AcuRite 02008 Weather Station with Reverse Color Display

This16878 popular weather station from AcuRite features an easy-to-read, illuminated reverse color LCD display. This weather station records and displays the indoor / outdoor temperature and humidity, barometric pressure history, and a clock and calendar. Features precise timekeeping that auto sets and updates for DST twice a year. Great gift item for weather enthusiasts!

See specifications:

Don’t Forget!

Daylight Saving Time ends November 2, 2014. If you want to avoid the hassle of turning your clocks back one hour, turn to Atomic timekeeping!

Find the perfect atomic clock for you at

The Future of Precision Timekeeping

In the beginning, time was a relatively abstract concept that was simply measured by the position of the sun and/or stars. It wasn’t very accurate, but it served a purpose.

Over a thousand years ago, the clock was no more than a dripping water vessel that improved timekeeping accuracy by a few hours. By 1300, the first mechanical timekeeping device was developed, improving accuracy to the hour (within 15 minutes or so). The 1600’s saw the introduction of the pendulum and spring driven movements, and minute hand, which improved timekeeping accuracy to mere minutes per day.

The late 1920’s gave way to the quartz movement, improving accuracy to one half a second per day. A little over 20 years later, the development of the atomic clock improved accuracy to 1 second in about 138 million years (give or take a day). This led to atomic clock movements for retail purchase, which automatically receive radio signals from Fort Collins, Colorado to keep precise time.

What’s Next?

Photo from

Can we get more accurate than atomic timekeeping? The answer is yes, although the means by which might surprise you. The year 2011 could well be marked as another significant year in the timeline of precision timekeeping with the development of the pulsar clock in Poland.

The pulsar clock is the first clock to measure time using a signal source from outside the Earth. It consists of a radio telescope that receives signals from selected pulsars, which are the remnant stars left-over from giant super-star explosions that took place long ago.

As any star continues to burn its fuel, it converts lighter elements (such as hydrogen and helium) to heavier and heavier elements. Eventually, stars reach a breaking point where they cannot convert the heavier elements (typically iron). Larger stars, much larger than our own sun, become increasingly unstable.

These massive stars basically collapse under the weight of their own gravity, as nuclear fusion is unable to sustain the core running out of fuel. The result is a massive explosion of the outer layers of the star, while the inner layers collapse into either a black hole or a neutron star under intense gravity.

If the core should happen to collapse into a neutron star, the remnant neutron star generally has a very high speed of rotation. For some, a beam of radiation is emitted along the magnetic axis of the star, yet the beam spins along with the rotation of the star. Since magnetic axis will generally differ from actual rotational axis, the stars can appear to flash, or “pulse”, which is how pulsars get their name.

In a sense, they are a cosmic lighthouse of sorts, continually rotating (pulsing) at accurately measurable intervals. For some “millisecond” pulsars, pulsars which basically rotate extremely fast, the regularity of pulsation proves to be more accurate than that of the atomic clock (about 5 times more accurate, improving precision to +/- 1 second in over half a billion years).

Are Pulsars the Future?

Could this become a regularity for timekeeping in the future, where radio receiver clocks latch onto the signal of a pulsar clock for accurate time? Pulsars will continue to rotate at regular intervals for millions and millions of years, and there is certainly no shortage of them as we continue to probe into the cosmos beyond our solar system.

It seems only fitting… And yet, it would also be a cosmic irony in a sense, considering the fact that our timekeeping endeavors first began with the stars so long ago.

Written By: Chris Akright

Chris is responsible for the kit, plan, and finishing technical support, which he has provided to Klockit customers for over 14 years. Chris also contributes new product designs, composes written/illustrated assembly manuals, and works to develop new kit and plan products for the Klockit catalog. Chris’s experience is the culmination of years of training under his mentor, and Klockit Designer, John Cooper.