Updated October 15, 2019 by Brett Dvoretz

The 10 Best Atomic Clocks

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This wiki has been updated 18 times since it was first published in June of 2015. Somewhere in the world, a single atom of caesium-133 is oscillating and, when it does it 9,192,631,770 times, that is the definition of a precise second in time. This kind of precision can be yours with a simple purchase of one of the useful atomic clocks on our list. We've rated them by accuracy, features, and lifespan, so you'll never have an excuse to be late again. When users buy our independently chosen editorial selections, we may earn commissions to help fund the Wiki. Skip to the best atomic clock on Amazon.

10. Marathon Jumbo CL030025

9. La Crosse Wall WT-3143A

8. Oregon Scientific Proji

7. Britta Products Franklin CL-1

6. Hito htc8376

5. Marathon CL030054B

4. Forestime Digital

3. La Crosse Technology Forecast Station 308-141

2. Hito HT1602

1. X-Sense Weather Station

Editor's Notes

May 20, 2019:

In addition to helping keep you on time, atomic clocks can boast an array of other features that make planning and going about your day easier, and we wanted to select models that show that. The Hito HT1602 lets you set two alarms, so you can set one for your wakeup time and another for an afternoon reminder. The Marathon CL030054B warns you when it's too hot to step outside, so you don't have to learn the hard way by going outdoors and potentially suffering a heat stroke. The X-Sense Weather Station even shows the local weather forecast, helping you know when to pack an umbrella or sunscreen. Your clock isn't much good if you can't see it well, so visibility was important, too. The Oregon Scientific Proji both projects the time onto the ceiling, as well as shows it on its face. Meanwhile, the Britta Products Franklin CL-1 has a liquid crystal display that's easy to see in daylight. Both the Hito htc8376 and the Hito HT1602 have good back lights for nighttime visibility. We considered both large, stationary models and compact portable ones, too, so the analog-style La Crosse Wall WT-3143A and the stylish Marathon Jumbo CL030025 caught our attention for nice home or office choices. For timekeepers on the go, the Hito htc8376 is a nice compact choice.

The Invention Of The Atomic Clock

The first atomic clock that tracked the passage of time accurately, was built in 1955 by Jack Parry and Louis Essen.

The concept of measuring time by atomic transition was first proposed in 1879 by Lord Kelvin, but the technology wasn't yet on par with philosophy. It wasn't until over 50 years later when magnetic resonance was developed by Isidor Rabi, that an actual method for doing this emerged.

In 1945, he first publicly proposed that atomic beam magnetic resonance could be used for timekeeping. Just four years later in 1949, a functioning atomic clock was built at the U.S. National Bureau of Standards, which is currently known as the National Institute of Standards and Technology. It was an ammonia maser device and it was actually less accurate that existing quartz time clocks. It did demonstrate the feasibility of the concept though and promoted further research.

The first atomic clock that tracked the passage of time accurately, was built in 1955 by Jack Parry and Louis Essen. It was constructed at the National Physical Laboratory in the U.K. and used a caesium standard, which was based on a transition of the caesium-133 atom. The astronomical time known as ephemeris time (ET) was used to calibrate the caesium standard atomic clock because, at the time, it was the most accurate fundamental unit of time.

Basing the atomic clock on the caesium-133 atom led to the internationally agreed definition of the SI second. It being the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two energy levels of the caesium-133 atom.

The Science Behind An Atomic Clock

The trick to counting time is by tracking the intervening span of time between something that occurs repeatedly with little, or preferably no, variation. Unfortunately, even the most precise quartz-crystal based clocks and mechanical pendulums will have slight discrepancies.

For this reason, the best method of keeping time is tracking the naturally occurring and exact vibrations in an energized atom. If exposed to specific radiation frequencies, electrons that orbit an atom's nucleus oscillate back and forth between different energy states. This is the basis for how atomic clocks track the passage of time.

A detector at the other end of the tube is then used to track the number of atoms that have changed their energy state.

Following the laws of quantum physics, all atoms emit or absorb electromagnetic energy when changing states. For every atom of a given element, all resonant emission frequencies are identical. Since caesium-133 atoms radiate energy at a fixed known frequency, their magnetic resonance can be used as a reference for tracking time in an incredibly accurate manner.

Inside of an atomic clock, caesium-133 atoms are sent down a tube and pass through radio waves transmitting at 9,192,631,770 cps. This causes them to resonate or vibrate and change to a new energy state. A detector at the other end of the tube is then used to track the number of atoms that have changed their energy state. The more tuned the frequency is to 9,192,631,770 cps, the more resonating caesium-133 atoms reach the detector. This information is then fed back into the radio wave generator and it synchronizes the radio waves frequency to match the one that created the highest number of caesium atoms striking the detector. This frequency is then counted and a second will be ticked off when the correct frequency count is met.

Though we have different types of atomic clocks these days, it doesn't matter whether they are based on hydrogen atoms, caesium atoms, or rubidium gas, the basic principal of how they work remains the same.

The Most Accurate Atomic Clock In The World

Atomic clocks have been incredibly accurate since they were first perfected in 1955, but scientist have worked hard since then to produce more and more accurate versions. The most recent record-breaking atomic clock doesn't lose even lose or gain one second in 15 billion years - which is the estimated age of the universe.

Unlike previous versions that could only be operated at cryogenic temperatures, this new one functions at room temperature.

This new clock was developed at the Joint Institute for Laboratory Astrophysics (JILA) and is based on the oscillation of strontium atoms. It roughly three times more precise than the previous record holder, which wouldn't have lost or gained a second over a 5 billion year period. It is expected that this strontium-based atomic clock may one day become the standard on which the world's official time is based.

There have been previous strontium-based atomic clocks, but the newest one has improved on them by eliminating measurement errors resulting from external sources of electromagnetic radiation by placing radiation shields around the device. They have also placed platinum thermometers inside of the vacuum tube to account for the extra heat generated. Unlike previous versions that could only be operated at cryogenic temperatures, this new one functions at room temperature. The JILA clock is also precise enough to reveal the tiny shifts in time that were predicted by Einstein's theory of relativity.

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Brett Dvoretz
Last updated on October 15, 2019 by Brett Dvoretz

A wandering writer who spends as much time on the road as in front of a laptop screen, Brett can either be found hacking away furiously at the keyboard or, perhaps, enjoying a whiskey and coke on some exotic beach, sometimes both simultaneously, usually with a four-legged companion by his side. He has been a professional chef, a dog trainer, and a travel correspondent for a well-known Southeast Asian guidebook. He also holds a business degree and has spent more time than he cares to admit in boring office jobs. He has an odd obsession for playing with the latest gadgets and working on motorcycles and old Jeeps. His expertise, honed over years of experience, is in the areas of computers, electronics, travel gear, pet products, and kitchen, office and automotive equipment.


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