rainbow

This is, without doubt, the best-known and most spectacular optical phenomenon of all those occurring in the atmosphere. The phenomenon's name refers to the goddess Iris, considered in Ancient Greece to be the messenger of the gods. Her comings and goings between Olympus - the dwelling of the gods - and the earthly world - where we human beings live - is well reflected in the rainbow and its apparent connection between sky and earth. We can define it as a large, semicircular luminous band, or a fraction of it, formed by a set of concentric arcs, overlapping one another, that display the colors of the visible spectrum of light. Red appears at the upper edge of the rainbow and violet at the lower one. This description corresponds to that of the primary or main rainbow, but, at times, the secondary rainbow and supernumerary arcs can also be seen. The appearance of all of them is due to the phenomena of refraction, reflection, diffraction, and interference of light as it passes through a curtain of raindrops illuminated by the sun or moon. Although it is common to refer to the seven colors of the rainbow, in reality the multicolored band is formed by a continuum, so that division is arbitrary.