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THE SPEED OF LIGHT =
299,792,458
(m/s)
meters per second
The speed of light =

299,792,458 meters per second, (exactly),or

299, 792.458 kilometers per second, (exactly).

We usually round that off to

300,000,000 meters per second, or

300,000 kilometers per second, or

186,000 miles per second.

In scientific notation







The speed of light = 299,792,458 m/s (exactly),

which you can find out by typing "speed of light" into the
Google search box.

There are several websites which have information about
this. See:

http://en.wikipedia.org/wiki/Speed_of_light

http://www.ldolphin.org/chistory.html

http://physics.nist.gov/cgi-bin/cuu/Value?c


Adobe Portable Document Format (PDF) file:

http://nvl.nist.gov/pub/nistpubs/sp958-lide/191-193.pdf


The number given above, the speed of light = 299,792,458
m/s, is not a measurement, but a DEFINITION.

After measurements of the speed of light had gotten to the
point of measuring fractions of a meter, it was decided to
simply redefine the meter.

The second had already been redefined in 1967, as a certain
frequency of atoms; (in the System International).

'The SI second is defined to be “the duration of
9,192,631,770 periods of the radiation corresponding
to the transition between the two hyperfine levels of
the ground state of the caesium 133 atom.”'

(spelled either cesium or caesium).

See:

Adobe Portable Document Format (PDF) file:

http://www.boulder.nist.gov/timefreq/general/pdf/1497.pdf

I don't pretend to understand how the second is measured,
or anything else on that web page, but I thought I should
include a reference.

So, once the second was determined exactly by this
scientific method, and the measurement of the speed of light
reached a precision of less than one meter, it was decided to
redefine the meter.

This was done in 1983.  

1983
"On October 20, the meter was redefined again. The
definition states that the meter is the length of the path
traveled by light in vacuum during a time interval of
1/299,792,458 of a second. The speed of light is

c = 299,792,458 m/s

The second is determined to an uncertainty,
U = 1 part in [10 to the 14th power] by the Cesium clock."

(spelled either cesium or caesium).

See:

http://www.mel.nist.gov/div821/museum/timeline.htm

I found out how to type subscripts and superscripts in the
Word program, but it doesn't work in the SiteBuilder program.
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