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The Most Accurate
Clocks in the World
How
do you know what time it really is? Have you ever looked at the clock
on your wrist, and it says noon ... lunch time! But the clock on the wall
says it's five minutes until noon. Don't you wish there was a way that
all time could be the same? Accurate time affects much more than
just getting to lunch on time or five minutes early. Transportation,
communication, manufacturing, electric power, and other technologies are
all extremely dependent on time. As our obsession with time grows, we
race to find the most accurate way to measure it. Scientists
have been working on a solution to this problem for decades. And they have found
the beginning of an answer.
R
ight now, the ATOMIC CLOCK is the most accurate time measuring
device in the world. While pendulums and crystal quartz clocks are
thought to have been very accurate, they are affected by the environment
that surrounds them. For example, humidity affects the functions
of a quartz watch. For these clocks to perform accurately, they must
constantly be measured and fixed. So scientists have been interested
in finding things in nature that are regular and dependable.
The Earth goes around the sun in about 365 days, the moon goes through
a cycle about every month, and, until recently, the geyser Old Faithful
shot out steaming water about every 15 minutes every day. But scientists
want absolute accuracy. Investigating the natural vibrations of atoms
seems to
be the best the answer. An atom vibrates at very regular intervals
in nanoseconds. One nanosecond is a billionth of a second, so it
takes one billion nanoseconds to make one second (for our British friends,
Americans use billion to refer to one thousand million).
There
are many atomic clocks that vary according to the natural element on which they
are based (for example, hydrogen, ammonia, or cesium). All natural
elements absorb and release electromagnetic radiation at a certain fixed
frequency. In simple terms, atomic clocks are electronic devices
that can measure time by counting the number of times atoms vibrate.
Because many different types of elements are used for atomic clocks,
the clocks work in different ways. However, they all rely on the fact
that atoms "take in" and "shoot out" electromagnetic rays at a stable frequency.
Cesium atomic clocks are one of the most accurate and most commonly used
types of atomic clocks. The picture above is a
very old cesium atomic clock.
To
give you an idea about the size of a laboratory Cesium atomic clock, it
is about the size of a railroad flatcar. The picture to the left
shows examples of laboratory atomic clocks. These are even a bit small compared
to others. A Cesium atomic clock called the NIST-7, or National Institute
of Standard Technology, is stationed in Boulder, Colorado. The cesium
clock in Boulder
is the most accurate clock on Earth to date; it is used as the official clock
of the United States. If you're tired of the inaccuracy of the clocks around
you, just adjust all your clocks to the NIST-7 standard time.
The other type of atomic clocks are Commercial
Cesium atomic clocks. They are about as large as a suitcase, although the size
varies. Some of these clocks are used in scientific laboratories, but
most are for public use. The picture to the right is an example
of a commercial atomic clock.Although
the commercial Cesium clocks are cheaper, they're still accurate and precise
within their time measurement functions. Some Cesium clocks are used
to synchronize other types of clocks. To give you an idea about the
accuracy of an atomic clock, a Cesium clock only loses two nanoseconds a
day or one second in 1,400,000 years.
How They Work
(A Complicated Explanation)
In 1955
after decades of scientific research, the first Cesium atomic clock was built.
It is the most accurate time measuring device to date. The way
these clocks work is very complicated. The first thing
that occurs is that liquid Cesium is put into an oven and heated until
it changes into a gas. Cesium atoms escape at very high speeds through
a hole in the oven. The speeding atoms now pass between two
electromagnets
that split the atoms into two beams: one in a high energy state and one in a low energy
state. The beams in the low energy state go through a U-shaped hole
where they are exposed to radiant energy by microwaves of very specific
wavelengths. Once again, the altered atoms are heated up and excited.
Many of the lower atoms are excited to a higher energy state. These
beams continue through some more electromagnets and are once again divided.
The atoms that are now in the high energy state pass a hot wire and become
electrically charged. The now-pure atoms are directed onto an electron
multiplier. The measurement of an atom's resonance frequency is then
found by adjusting the frequencies of the microwaves, and the electron
multiplier is intensified to the highest degree. This frequency is
put into a feedback control circuit, which is connected to a quartz crystal
oscillator (like a quartz watch that's set at a certain frequency). This
makes a pulse almost exactly once every second.
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Although
the commercial Cesium clocks are cheaper, they're still accurate and precise
within their time measurement functions. Some Cesium clocks are used
to synchronize other types of clocks. To give you an idea about the
accuracy of an atomic clock, a Cesium clock only loses two nanoseconds a
day or one second in 1,400,000 years.
