Light and sound waves are very different. In Aviation, we fly aircraft based on the speed of sound using the Unit of Mach; named after the Austrian Physicist. Airliners will typically switch to Mach pushing through the upper 20 thousand feet, the reasoning being because the density is low enough that we can get a more accurate reading of speed based on Mach number. The speed of sound changes with pressure and temperature. On the contrary, the speed of light is constant. From celestial navigation or even space exploration, we calculate distance in light years. It travels through the void of space. Light waves travel much faster