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. At the same time an observer freefalling into that black hole measures the speed of light locally (in his location) at 299792.458 km/s; when he looks towards the black hole he sees the speed of light there much slower; when he looks away from the black hole he sees the speed of light there much faster. When he looks towards outside gravitational fields he sees the speed of light there a zillion km/s. In 1915 (10 years after Special Relativity) Einstein developed another theory called General Relativity that deals with gravitational fields and according to this latest theory the speed of light appears to vary with the intensity of the gravitational field. Learn more.

Effective Speed of Light

Expansion of Universe and its effect on measured Speed of Light: Dark Energy

Scientists just confirmed the existence of "Dark Energy", a mysterious repulsive force that acts in opposite to gravity. Scientists today do not know what this "Dark Energy" is but they know that it is causing the entire universe to expand at an increasing rate. This Dark Energy is even causing distant galaxies to recede from us faster than our local speed of light. This expansion is causing light en route to be dragged away from us. This makes observers to see distant inbound light at effective speeds less than 299792.458 km/s and to see distant outbound light at effective speeds greater than 299792.458 km/s. However every inertial observer measures the speed of light locally (in his location) at 299792.458 km/s in any direction. Learn More

Speed of Light = 12000 Lunar Orbits/Earth Day

Inertial Earth-Moon System gives: Speed of Light