Electro magnetic waves do not require a material medium to expand . They include, among others, visible light and radio waves , television but they also are produced by the sun in a certain frequency(30PHz). All propagate in vacuum to a constant, very high (300 0000 m / s ) but not infinite speed . Therefore that is why we can see a the light of a star that have already disappeared.
History of thelcetromagnetic waves
Heinrich Hertz discovered electromagnetic waves in the years 1885–1889. 150 years ago. James Clerk Maxwell, developed a scientific theory to explain electromagnetic waves. He noticed that electrical fields and magnetic fields can couple together to form electromagnetic waves, the same as rubbing your feet on a rug to create static energy.Uglielmo Marconi an Italian physicist used Heinrich Hertz's discovery of radio waves in 1888 transmitted electronic signals from his family home in Pontecchio more than a mile away.
FUNNY FACTS
.Em waves are the only type of wave that can travel through empty space.
.All EM waves are transverse, and are not mechanical.
.Infrared wavelengths have just a little bit longer wavelengths then the color red on the visible electromagnetic spectrum.
.Gamma waves are the most energetic type of wave in the Electromagnetic Spectrum.
.Ultraviolet waves have just a little bit smaller wavelength then the color violet on the visible electromagnetic spectrum.
.Micro waves can be used for radar as well as cooking food.
.Gamma waves can be very dangerous.