Realizing this meant that the speed of light is finite,
Rømer calculated it using accumulated difference
between actual and predicted eclipse times.
Historical speeds
Rømer’s result in 1676
was 26.6% slower than the true speed of light.
James Bradley’s result in 1729
was 0.4% faster.
Hippolyte Fizeau’s result in 1849
was 5.07% faster.
Léon Foucault’s result in 1862
was 0.6% slower.
Rosa and Dorsey’s result in 1907
was less than 0.03% slower.
In a vacuum
It’s somewhat crude today to say
outer space is a perfect vacuum.
It’s a sea of all kinds of things.
And the speed of light in an atmosphere
depends on altitude, temperature,
and whether the light’s continuous or pulsed.
Do absolutes exist in real life?
We can never judge nor be judged
in a vacuum. Take it with a grain of salt.
The speed of light, c, is exactly 299,792,458 meters per second,
about 186,282 miles per second.
Only luxons—photons, gluons, and, theoretically, gravitons—can travel at this speed.
Anything with “rest mass,” according to the special theory of relativity,
gains “relativistic mass” as its speed approaches the speed of light,
which it can not reach.
The numeric value of c in meters per second
is fixed by the definitions of meter and second.
The speed of light, c, is exactly 299,792,458 meters per second, about 186,282 miles per second. Only luxons—photons, gluons, and, theoretically, gravitons—can travel at this speed. Anything with “rest mass,” according to the special theory of relativity, gains “relativistic mass” as its speed approaches the speed of light, which it can not reach.
The numeric value of c in meters per second is fixed by the definitions of meter and second.
See also in The book of science:
Readings on wikipedia: