Rainbows Essays - Rainbow, Moonbow, Observational Astronomy, Sky

Rainbows A rainbow is one of our atmosphere's most exquisite and marvelous creations; "one of the most spectacular light shows observed on earth" (Ahrens, 1998). When a person views a rainbow, they are getting a personal light show that no other person can see as they do. Humphreys points out that: "Since the rainbow is a special distribution of colors (produced in a particular way) with reference to a definite point - the eye of the observer - and as no single distribution can be the same for two separate points, it follows that two observers do not, and cannot, see the same rainbow." (Humphreys, 1929). Of course, a camera lens will record an image of a rainbow which can then be seen my many people (Lynds, 1995). A rainbow is essentially made up of seven brilliant colors: red, orange, yellow, green, blue, indigo, and violet; moreover, it is comprised of many coloration that the eyes cannot see. No painter can manufacture the colors of the rainbow, for they create color by mixing, but no mixing will give red, green, or purple. These are the colors of the rainbow, though between the red and the green an orange color is often seen (Aristotle, 350 BC). To understand how the awesome production of a rainbow occurs is a feat of physics and mathematics. The two most important ingredients are light and drops of water. The manner and position in which the light and water droplets transverse, and the reactions between the two, are complex formulas of nature. Additionally, certain circumstances make it possible for a rainbow to occur. You cannot have a rainbow without some source of light. It is possible to create an artificial rainbow utilizing artificial light, but for this paper, I will only use instances and circumstances of naturally occurring light which produce naturally occurring rainbows. The sun is nature's primary source of rainbow creating light; however, occasionally, the light of the moon can produce a rainbow. For a lunar rainbow to occur the conditions have to be just right. The moon has to be a full moon, which only happens once a month. The light of a full moon is a faint light, so the lunar rainbow will never be as prominent as the solar rainbow. Additionally, the full moon has to be either rising or setting. A naval officer, V. E. Mikkelson, described his reaction when he learned that the spotlight he saw was actually a lunar rainbow: The strange phenomenon I was viewing was a rainbow generated by moonlight! It was being formed by moonlight passing through rain trailing from one of the fluffy cumulus clouds. The rainbow was composed of the standard colors, but they were softer and paler than those generated by direct sunlight. They were what I can only describe as pastel. I was truly entranced. I have seen many of nature's beauties, but none have ever impressed me so powerfully (Mikkelson, 1994) This is a rare phenomenon. Captain Mikkelson has been a seaman for over twenty years and has only viewed this one lunar rainbow; moreover, he has spoken to numerous career seamen and none reported ever seeing such a magnificent sight. Another essential component of the rainbow is drops of water. Again, water drops from sprinklers or the sprays emitted from waterfalls can produce a rainbow, but I will focus on water drops that fall from the sky. A raindrop is nature's reflective mirror in the sky. The smooth, yet internally curved, surface of a raindrop can refract and reflect light. A typical raindrop is spherical in dimension and thus has a symmetrical effect on light. Lynds (1995) points out that the "purity" of the colors of the rainbow depends on the size of the raindrops. Large drops (diameters of a few millimeters) give bright rainbows with well defined colors; small droplets (diameters of about 0.01 mm) produce rainbows of overlapping colors that appear nearly white. When it rains, the droplets are never the same exact size and shape; thus, a rainbow occurs in a range of colors. Sunlight slows and bends when it enters a raindrop. Some of the light strikes the back of the drop at such an angle that it is reflected within the drop, this is the critical angle of 48?. Any angle greater than this and the light bounces off the back of the raindrop and is internally reflected towards our eyes. Each light ray bends differently from the others, so each angle is slightly different; therefore, the light is dispersed into a