Atmospheric Optical Phenomena

If Earth's atmosphere were a vacuum, the only atmospheric optical phenomenon observable would be a stream of white light from the sun. The fact that colors appear in the atmosphere is a consequence of the way that white light is broken up into its component parts—red, orange, yellow, green, blue, indigo, and violet: the spectrum—during its interaction with materials in the atmosphere. That interaction takes one of three general forms: reflection, refraction, and diffraction.

Reflection occurs when light rays strike a smooth surface and bounce off at an angle equal to that of the incoming rays. Reflection can explain the origin of color in some cases because certain portions of white light are more easily absorbed or reflected than are others. For example, an object that appears to have a green color does so because that object absorbs all wavelengths of white light except that of green, which is reflected.

One form of reflection—internal reflection—is often involved in the explanation of optical phenomena. During internal reflection, light enters one surface of a transparent material (such as a water droplet), is reflected off the inside surface of the material, and is then reflected a second time out of the material. The color of a rainbow can partially be explained in terms of internal reflection.

Refraction is the bending of light as it passes at an angle from one transparent material into a second transparent material. The process of refraction accounts for An aurora borealis display. Photograph by Pekka Parviatnen. © Pekka Parviatnen. Photo Researchers, Inc. Reproduced by permission. the fact that objects under water appear to have a different size and location than they have in air. Light waves passing through water and then through air are bent, causing the eye to create a visual image of the object.