2. Radiation

2.1 Types of radiation

The radiation we'll be dealing with here is a very small part of the vast spectrum of electromagnetic radiation, whose wavelengths range from kilometers (longwave radio), to meters (frequency modulation), to microns (from 0.38 to 0.78 µ for the visible, from violet to red) and even further to X-rays and gamma rays (figure 1 ). Solar radiation ranges from 0.3 to 2.5 µ. The radiation that is useful for what follows is called "long-wave radiation", from around 5 to 50 µ.