Fog BowAs the water droplets which form the rainbow colors get smaller, the colors begin to disappear. In fine mist, all colors except violet may disappear. Even finer fog droplets, smaller than 0.05 mm, produce the white rainbow or fog bow. "Fogbows frequently appear as ghostly arches over a dark section of a foggy country road when you stand with a streetlight to your back. Natural fogbows may be lit by the low, red sun at dawn." Schaaf has a detailed description of examples of fog bows in his Wonders of the Sky, Chapter 1.
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Dew Bow"Dewdrops...are large enough so that the bizarre, hyperbola-shape dewbow seen lying on dewy grass after sunrise shows all the rainbow's colors. The hyperbola results from the flat ground intersecting the 42°-radius cone of the rainbow, the apex of which is at your eye. If the dew lasts well into the day, the dewbow will become a parabola and then an ellipse as the Sun gains altitude." Schaaf
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Moon BowIf the light from the moon strikes falling water droplets, the primary rainbow is produced just as it is produced by sunlight, except that moonlight is some times less intense. Since the vision which perceives such low light levels is primarily rod vision which is not color sensitive, the moon bow appears white.
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