Astronomically, the optical runs from 300-1000nm. Some of this penetrates the atmosphere, mostly at wavelenths less than 10 microns. This can be felt as heat. The atmosphere is transparent to radio waves at wavelengths longer than a few tenths of a mm and shorter than a few hundred meters. Astrophysical radio waves are generated mostly by electrons oscillating in a magnetic field, processes similar to those we employ to generate AM and FM radio signals.
All waves have the property that, once emitted, they propagate outwards from the source.
As they do so the energy density in the wave decreases. This is because the total energy in the wave is fixed, while the volume of space the wave is expanding into is continuously increasing. Electro-magnetic waves expand spherically out into space. At any time the wave occupies the surface of a sphere. We can use the inverse square law to set up a scale of absolute magnitudes .