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The Epic Interactive Encyclopedia 1998
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Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso
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Atomic_clock
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1992-09-03
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An atomic clock is a timekeeping device
regulated by various periodic processes
occurring in atoms and molecules, such as
atomic vibration or the frequency of absorbed
or emitted radiation. The first atomic clock
was created at the US National Bureau of
Standards in 1948. Atomic clocks are so
accurate that minute adjustments must be made
periodically to the length of the year to
keep the calendar exactly synchronized with
the Earth's rotation, which has a tendency to
speed up or slow down. There have been around
20 adjustments made to the atomic clock since
1972. In 1992 the northern hemisphere's
summer was one second longer than usual.
An extra second was added to the world's time
at precisely 23 hours, 59 minutes and 60
seconds on 30 June 1992.
Subject by: Vince Pike