The 10 Best Atomic Clocks

Updated March 16, 2018 by Sheila O'Neill

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We spent 43 hours on research, videography, and editing, to review the top choices for this wiki. Somewhere in the world, a single atom of caesium-133 is powering through millions of cycles of radiation that someone decided is the definition of a single second in time. This kind of precision can be yours with a simple purchase of one of the 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 picks, we may earn commissions to support our work. Skip to the best atomic clock on Amazon.

10. Sangean Analog

The Sangean Analog features a large LCD screen with adjustable brightness settings, 14 radio station presets, and a dual alarm to get you up on time. You have the choice of waking up to either music or a hard-to-ignore buzzer.
  • input for mobile devices
  • good sound quality
  • instructions are poorly written
Brand Sangean
Model RCR-3
Weight 3.9 pounds
Rating 3.7 / 5.0

9. AcuRite Projection

With its innovative ability to display the time on your wall or ceiling, the AcuRite Projection provides accuracy, clarity, and style when viewed from all directions. It is designed to run off AC power, but has a backup battery, too.
  • programmable alarm with snooze
  • built-in usb charging port
  • brightness settings need improvement
Brand AcuRite
Model 13021
Weight 9.6 ounces
Rating 4.0 / 5.0

8. La Crosse Wall

If digital displays aren't your thing, La Crosse Wall might be the answer for you. It has a handsome 14-inch diameter face with automatically setting features for things like daylight savings, yet appears to be a simple, traditional, analog clock.
  • very easy to set up
  • works in all 4 us time zones
  • signal strength could be better
Brand La Crosse Technology
Model WT-3143A-INT
Weight 3 pounds
Rating 3.8 / 5.0

7. Marathon Panoramic

The Marathon Panoramic is a self-setting and self-adjusting option that has an impressively easy-to-read, 4-inch-tall display, and offers state-of-the-art styling suitable for the most modern home or office. It shows the temperature, date, and more.
  • smooth brushed silver design
  • good price for the quality
  • numbers on the side are hard to read
Brand Marathon
Model SYNCHKG036784
Weight 1.3 pounds
Rating 3.6 / 5.0

6. Hito Bedside Travel

Good things often come in small packages, and the Hito Bedside Travel is no exception to this rule. Its compact design makes it perfect for packing in a tiny carry-on suitcase, but it's still high-quality enough to serve as a regular bedside companion.
  • soft amber led backlight
  • dims at night automatically
  • can be hard to see during daytime
Brand hito
Model htc8376
Weight 5.6 ounces
Rating 4.3 / 5.0

5. La Crosse Weather

La Crosse Weather looks equally stylish as either a wall unit or a desk clock. Its cherry panels frame a crisp, clean face with an attractive display that's easy to read, even at a quick glance. Its numbers are thick and bold.
  • provides weather forecasts
  • wireless temperature readings
  • low battery indicator
Brand La Crosse Technology
Model WS-8157U-CH-IT
Weight 1.9 pounds
Rating 4.8 / 5.0

4. Marathon Jumbo

The Marathon Jumbo offers a 12- or 24-hour display option in several time zones. Its size and sleek design make it easy and fun to view. This model is suitable for anywhere from the factory floor to a posh and modern living room.
  • c-cell batteries last a long time
  • available in multiple colors
  • folding stand is included
Brand Marathon
Model CL030025WD
Weight 4.4 pounds
Rating 4.8 / 5.0

3. AcuRite Home

The colorful display of the AcuRite Home is both pleasant to look at and highly informative. It comes with a wireless sensor meant to be put outside, so you can have accurate, up-to-the-minute information on what temperature it is from the comfort of your bed.
  • great connectivity range
  • 14 different weather icons
  • controls are simple and intuitive
Brand AcuRite
Model 02081M
Weight 1.6 pounds
Rating 4.5 / 5.0

2. Hito Self-Setting

Featuring a decent backlight on its face and a large screen that lets you read the time from any angle, the Hito Self-Setting offers convenience and functionality at their best. It can be wall mounted or can sit on a desk using its built-in kickstand.
  • can set two different alarms
  • works on two c batteries
  • good choice for senior citizens
Brand hito
Model HT1602
Weight 1.5 pounds
Rating 4.6 / 5.0

1. La Crosse 16 Inch

La Crosse 16 Inch might just be the last clock you ever need to buy. It sports a supremely large display that's perfect for conference rooms, kitchens, classrooms, and more. It also features auto-updating functions for daylight savings time.
  • optional manual override
  • hangs on walls or stands freely
  • alarm with 5-minute snooze
Brand La Crosse Technology
Model 515-1316
Weight 6.8 pounds
Rating 4.9 / 5.0

The Invention Of The Atomic Clock

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.

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.

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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Last updated on March 16, 2018 by Sheila O'Neill

Sheila is a writer, cosplayer, and juggler who lives in Southern California. She loves sitting down with a hot cup of tea and coming up with new ideas. In her spare time, Sheila enjoys drawing, listening to podcasts, and describing herself in the third person.

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