Chapter 3 - Solar radiation

Abstract

Of all the factors that control the weather, the sun is by far the most powerful. Practically, everything that occurs on the Earth is controlled, directly, or indirectly, by the sun. The sun affects the places humans inhabit, in the kind of homes that are built, the work that is done, and the equipment that is used. Less than one-millionth of the energy emitted from the sun's surface travels ninety-odd million miles to reach this planet. The sun's energy crosses those miles in the form of short electromagnetic radio waves, identical in nature to those used in broadcasting, which pass through the atmosphere and are absorbed by the Earth's surface. These waves warm the Earth's surface and are then re-radiated back to space. The wavelength of the energy emitted by the Earth is much longer than that emitted by the sun, because the Earth is much cooler than the sun. Radiation from the sun consists of three differing wavelengths: heat rays, actinic rays, and light rays. Heat rays and actinic rays are intercepted by solid bodies and produce peculiar effects in varying degrees according to the nature of the surface on which they fall. The light rays are responsible for daylight, and both light rays and actinic rays are necessary for the life processes of plants. The heat ray's most important manifestation is temperature. However, radiant energy can also damage equipment as heat rays can warm the material or its surrounding environment to dangerous levels and photochemical degradation of materials can be caused by the ultraviolet content of solar radiation.