Electromagnetic spectrum

The electromagnetic spectrum is often shown as a range of photon energies and their names. Since energy = frequency*speed of light and speed of light is a constant, as frequency goes up the energy of a photon goes up. So the highest energy photons have the highest frequency but the shortest wavelength. Apparently the equation E=hv was just a guess by Max Plank, at the time there was no experimental or theoretical justification for the equation.