1.Speed of light
The speed of light(actual value) is 299,792,458 metres per second
By 1665 another famous scientist, Robert Hooke, noted that Descartes' and Galileo's experiments failed to prove the instant propagation of light.
What they did prove, Hooke felt, was, that if light took time to travel from one point to another, it did so "exceeding quick." If, for instance, light took two minutes instead of two hours to go past Earth to the Moon and back to Earth, the deviation from straight line of Sun, Earth, and Moon during an eclipse would be too small to be detected. A similar argument could be raised against Galileo. If light took a very small fraction of a second to travel 10 miles, its motion would appear instantaneous. In other words, Galileo's and Descartes' observations were inconsistent with a comparatively slow speed of light, but they still left open the question whether light took unimaginably short time to travel great distances or whether it took no time at all to travel any distance. 
from one point to another, or whether it takes no time
at all had been resolved by the Danish astronomer,
Ole Roemer. Roemer provided the first clearcut proof
that light takes time to move from one point to another,
and the first reasonable estimate of its actual speed.
amazing!
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