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A unit of time equal to 1/60 of a
minute
or 1/3600 of an
hour
. The international definition was originally
1/86400th of a mean solar day in 1900, but is now instead the time required for 9,192,631,770 vibrations of a Cs atom.
Since the
speed of light
is
defined
to be 299,792,458 m s
-1
, this makes the
meter
a derived
unit. A mnemonic for the number of seconds in a
year
is 1 nanocentury is approximately equal to
seconds (1 y
=
s, whereas this approximation gives
s).
Day
,
Ephemeris Second
,
Hour
,
Minute
,
Week
,
Year
© 1996-2007 Eric W. Weisstein
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