Thermal Radiation of Earth
The earth's heat emission at long wavelengths,
measured during the month of January. The brighter colors show more heat
coming from the Southern Hemisphere during the height of its summer.
The invisible way of transmission of heat with out any physical contact between the source and the object is known as radiation.
Radiant energy is always in the form of electromagnetic waves. It includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays. The energy emitted by a body in the form of radiation on account of its temperature is called thermal radiation. All bodies emit thermal radiation continuously. The energy and wavelength of these radiations depend on the temperature and nature of the radiating body. All infra–red photography such as from weather satellites, night vision goggles, etc., are based on thermal radiation from all bodies.
Properties of thermal radiations are as follows:
- Thermal radiations can travel through vacuum.
- These radiations always travel along straight lines.
- Thermal radiations obey the laws of reflection and refraction
Thermal radiations obey the inverse square law. The intensity of heat radiation goes on decreasing as the distance from the source goes on increasing. If I is the intensity of thermal radiation and r is the distance from the source, then I is proportional to 1/r2.