I am going to have to disagree with Rogue49's earlier statement that "The Speed of light is constant" The speed of light is in fact not constant, but it does have a maximum value. That maximum value is known as C, but Light can be slower. Simply pass light though any object with an index of refraction greater than 1 and light is slowed. We know this because the measured frequency in the object is constant, but the wavelength of light changes. Using the equation velocity=frequency*wavelength, we find that with a constant frequency, a decrease in wavelenth will propagate to a decrease in velocity.
Isn't relativity fun!
