Short answers, pulled from the story.
William Herschel discovered infrared radiation in 1800 when he placed a thermometer beyond the red end of a sunlit prism and observed the mercury rise. This experiment proved the existence of invisible heat rays where no visible light could be seen. The discovery marked the beginning of a scientific journey revealing the universe is bathed in a vast, invisible river of energy.
James Clerk Maxwell published his four equations in the early 1860s to unify the theories of electricity and magnetism. He derived a wave form for the electric and magnetic fields and predicted that disturbances in the field would travel at a speed calculated from vacuum permittivity and permeability constants. His theory suggested that radio waves, infrared, and ultraviolet rays were all manifestations of the same phenomenon differing only in frequency and wavelength.
Max Planck proposed that energy is emitted in discrete bundles or packets called quanta in 1900 to solve the ultraviolet catastrophe. Albert Einstein took this idea further in 1905 by suggesting that light itself consists of real particles named photons. This quantum perspective explains why low-frequency radio waves can pass through walls while high-energy gamma rays can penetrate deep into biological tissue.
Electromagnetic radiation moves at the speed of light which is approximately 299,792,458 meters per second. This constant is intrinsic to the fabric of the universe and was later proven by Maxwell's equations. The waves travel as a self-propagating wave of the electromagnetic field where the electric field and magnetic field oscillate perpendicular to one another and to the direction of travel.
Earth's atmosphere acts as a selective filter that blocks most high-energy radiation while allowing specific bands to reach the surface. Molecular nitrogen and ozone absorb the majority of ultraviolet and X-rays to prevent the most damaging forms of ionizing radiation from reaching the ground. Visible light passes through air with minimal absorption while infrared radiation is absorbed by water vapor and carbon dioxide creating the greenhouse effect that warms the planet.