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299792458

299,792,458 meters per second, commonly denoted c, is the exact speed of light in vacuum in SI units. Under the 1983 redefinition of the International System of Units, c is fixed at this value, making it an exact constant and tying the unit of length to the unit of time.

Because c is fixed, the meter is defined as the distance that light travels in vacuum in

As an invariant, the speed of light plays a central role in physics and cosmology. It appears

1/299,792,458
of
a
second.
The
second
is
defined
by
the
cesium-133
atom's
hyperfine
transition.
in
Maxwell's
equations
and
Einstein's
theory
of
relativity,
and
serves
as
a
foundational
constant
in
metrology
and
technology.
The
value
299,792,458
m/s
is
used
directly
in
calculations
across
science
and
engineering,
and
its
exactness
underpins
the
modern
dimensioning
of
time
and
length.