Optics
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21 terms
Terms | Definitions |
|---|---|
 Reflection | Process whereby a surface turns back a portion of the radiation that strikes it. When the radiation that is turned back from the surface is visible light, the radiation is referred to as reflected light. |
| Scattering | Process by which small particles in the atmosphere deflect radiation from its path into different directions |
| Crepuscular Rays | Alternating light and dark bands of light that appear to fan out from the sun's position, usually at twilight |
| Refraction | The bending of light as it passes from one medium to another |
| Scintillation | The apparent twinkling of a star due to its light passing through regions of differing air densities in the atmosphere |
| Twilight | The time at the beginning of the day immediately before sunrise and at the end of the day after sunset when the sky remains illuminated |
| Green Flash | A small green color that occasionally appears on the upper part of the sun as it rises or sets. The thick atmosphere refracts sunlight, with purple and blue bending the most and red light the least. Because of this bending, blue light should appear along the top of the sun. But because atmosphere selectively scatters blue ight, very little reaches us, and we see green light instead. |
| Inferior Mirages | When the air near the ground is much warmer than the air above, objects may not only appear lower than they are, but also inverted. Inverted appearance because light reflected from the top fo the tres moves outward in all directions. Rays that enter teh hot, less-dense air above the sand are refracted upward, entering the eye from below. Brain fooled into thinking these rays came from below the ground. |
| Superior Mirage | In polar regions, air next to a snow surface can be much colder than the air many meters above. Because the air in this cold layer is very dense, light from distant objects entering it bends toward the normal in such a way that the objects can appear to be shifted upward. |
| Fata Morgana | Complex mirage that is characterize by objects being distorted in such a way as to appear as castlelike features |
| Halo | Rings or arcs that encircle the sun or moon when seen through an ice crystal cloud or a ksy filled with falling ice crystals. Halos are produced by REFRACTION of light. |
| Tangent Arc | An arc of light tangent to a halo. It forms by REFRACTION through ice crystals. |
| Dispersion | The separation of white light into its different component wavelengths |
| Sundogs (Parhelia) | A colored luminous spot produced by refraction of light through ice crystals that appears on either side of the sun. |
| Sun pillars | A vertical streak of light extending above (or below) the sun. It is produced by the reflection of sunlight off ice crystals. |
| Rainbows | An arc of concentric colored bands that spans a section of the sky when rain is present and the sun is positioned at the observer's back |
| Corona | A series of colored rings concentrically surrounding teh disk of the sun or moon. Smaller than a halo, this is often caused by the diffraction of light around small water droplets of uniform size. |
| Diffraction | The bending of light around objects, such as cloud and fog droplets, producing fringes of light and dark or colored bands. |
| Iridescence | Brilliant spots or borders of colors, most often red and green, observed in clouds up to about 30 degrees from the sun. Diffraction phenomenon. |
| Heiligenschein | A faint white ring surrounding the shadow of an observer's head on a dew-covered lawn. Forms when the sunlight, which falls on nearly spherical dew drops, is focused and reflectd back toward the sun along nearly the same path that it took originally. This light doesn't travel in exact path, but rather spreads out just enough to be seen as bright white light around the shadow of your head on a dew-covered lawn. |
| Glory | Colored rings that appear around the shadow of an object. Diffraction phenomenon. |
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