Curious, I googled "In the radio astronomy of Pulsars we find that the shorter wavelengths of the leading edge of the pulse arrive before longer wavelengths. Th

Curious, I googled "In the radio astronomy of Pulsars we find that the shorter wavelengths of the leading edge of the pulse arrive before longer wavelengths. The velocity of light, c, is NOT constant but varies by wavelength" and something interesting came up: "interstellar clouds of electrons retard the velocity of radio waves in direct proportion to their wavelength" in an article from a 1968 edition of Scientific American written by Anthony Hewish...the same guy who discovered pulsars