What is an atomic clock and how does it work?

What is an atomic clock?

Atomic clocks are extremely accurate clocks. They are better than any other type of clock at keeping time and are used to synchronize other clocks around the world. In the United States, the time standard is regulated by the Navy, which uses an atomic clock to keep the time.

So, what makes an atomic clock so accurate?

Traditional mechanical clocks keep time by having a part inside that moves back and forth, or oscillates, at a uniform rate of speed. The precision of an atomic clock comes from a system that uses the natural vibrations in an atom as an electrical oscillator. In an atomic clock, the nucleus of an atom and the electrons around it are responsible for the steady oscillation. It is important to note that atomic clocks are not radioactive; instead the name derives from this action within the atom that is used to track the passage of time.

As the electrons move around within the atom, a device is used to sense the changes in the energy level. Different types of atomic clocks use different devices for this purpose. In a cesium atomic clock, a beam of cesium atoms is affected to action by a magnetic field within the clock. In modern cesium clocks, laser beams are sometimes used to stop or slow the motion of the atoms.

Hydrogen atomic clocks use a container of high-energy hydrogen to keep the atoms active. Other atomic clocks use rubidium gas and detect the changes to its ability to absorb light. Since the frequency at which the atomic clock’s oscillations occur is extremely high, they cannot control the clock. So, a crystal oscillator that is much more stable is used to control the clock and the two systems are constantly compared to keep the crystal oscillator synchronized to the oscillation of the electrons.

Whichever method is used to make an atomic clock function, it constantly checks itself to keep time extremely accurately. The development of atomic clocks allowed a greater granularity of timekeeping than was ever before possible. Cesium atomic clocks only lose a one second increment per million years and hydrogen atomic clocks are even more accurate.

Why is accurate time so important?

While it does not matter to most people to have time accurate to a fraction of a second, there are many scientific and engineering uses of precision time. The radio signals broadcast by atomic clocks are used by global positioning and navigation systems and by the space program for tracking vehicles and space objects.

But, what about the atomic clocks they sell for home and office use?
There are a number of reasonably priced clocks on the market labeled as atomic clocks. These are not really atomic clocks, however, they do keep very accurate time. How do these clocks work?

The U.S. government has an atomic clock in Colorado that emits a radio signal. These atomic clocks are set to receive this radio signal and synchronize their time displays to the atomic clock time regularly. The more often the clock checks the radio signal and resynchronizes, the more accurate it will be.

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