Historical Measurement

Before the 17th century scientists believed that there was no such thing as the "speed of light". They thought that light could travel any distance in no time at all. Later, several attempts were made to measure that speed.

Speed of Light In Gravity

An observer outside gravitational fields measures the speed of light locally (in his location) at 299792.458 km/s but when he looks towards a black hole he sees the speed of light there to be as slow as a few meters/s.

12000 Lunar Orbits/Earth Day

When the geocentric frame is inertial 12000 Lunar Orbits / Earth Day becomes equivalent to the speed of light.