Short answers, pulled from the story.
Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits it; the emission arises from charge acceleration and dipole oscillation in the atoms and molecules of a material, converting kinetic energy into electromagnetic waves.
Astronomer William Herschel discovered infrared radiation and published his results before the Royal Society of London in 1800. He used a prism to refract sunlight and placed a thermometer beyond the red end of the visible spectrum, where the temperature rose despite no visible light being present.
Planck's law, first offered by Max Planck in 1900, describes the spectral distribution of electromagnetic radiation emitted by a blackbody at a given temperature. It established that energy is emitted in discrete quanta, each with energy equal to the Planck constant multiplied by the radiation's frequency, rather than as a continuous flow.
The Stefan-Boltzmann law states that the total emissive power of a blackbody rises as the fourth power of its absolute temperature. Josef Stefan inferred it in 1884 from John Tyndall's experimental measurements, and Ludwig Boltzmann derived it from statistical principles in the same year.
The Draper point is the temperature of approximately 798 K at which virtually all solid or liquid substances begin to visibly glow with a dull red color. Below this temperature, incandescence still occurs but is too weak in the visible spectrum to be perceptible to the human eye.
At distances below the thermal wavelength, heat transfer can surpass the limits set by Planck's blackbody theory, a finding first established by Sergei Rytov in 1953 using the fluctuation-dissipation theorem. When emitter and absorber support surface polariton modes that couple across ultra-narrow gaps of microns or nanometers, the deviation from Planck's law can reach several orders of magnitude.