THERMAL AND NONTHERMAL RADIATION
Thermal radiation from the planets, which is due to the fact that the planets are hot, can be studied far into the infrared with today's heat-sensing instruments. This radiation is blackbody radiation, caused by the random thermal motion of the particles that compose the outer parts of the planets. Thus astronomers may apply Planck's law, the Stefan-Boltzmann law, and Wi en's law to such radiation. The data obtained from infrared radiation provide important information on surface and atmospheric temperatures and, indirectly, chemical composition.
Nonthermal radiation is radiation due to physical processes other than that involved in producing blackbody radiation. That is, it owes its explanation to some other fact than that the planet is hot. For example the light produced in lightning is nonthermal radiation. The planets' normal thermal radiation and any nonthermal radiation present are often observable with radio telescopes in the regions of millimeter, centimeter, and meter wavelengths.
