A ordinary rainbow is an amazing natural phenomenon - but a smiley rainbow? That is definitely something special and unless you live in the Polar regions, something you may never see in your lifetime. But before we go any further, let's examine how normal rainbows occur.
It was Sir Isaac Newton who discovered that white light is actually the combination of seven colors in the right proportions, each with a different wavelength. When this light hits another surface and refracts or bends,the different wavelength of each color causes them to bend in different proportions, resulting in seven separate colors.
This is the reason we see rainbows. The white light from the sun refracts when it comes in contact with the raindrops and breaks up into the seven colors; red, orange, yellow, green, blue and violet. Red, which has the longest wavelength, bends the least and is therefore always the outer ring of the rainbow, while violet, which has the shortest wavelength, bends the most and always ends up as the innermost ring.
The inverted or smiley-face rainbow works on the same principle of white light separating into seven colors, but is formed quite differently. For an inverted rainbow or circumzenithal arc as it is also called, to occur, the sky must be clear of rain and low-level clouds. The sun has to be shining at a certain angle and the cirrus clouds high in the atmosphere must be laden with flat, six-sided ice crystals that act as a field of prisms. The sun's rays enter the ice crystals and refracts through them, projecting an arc in the sky, that look like the skies are smiling down on us. As would be expected, the colors are reversed too - the first color is violet, while the last color is red.
According to metereologists, circumzenithal arcs are fairly common in high altitudes, but are often not visible due to low hanging clouds. Therefore, when you see a rainbow that smiles, it is truly a special day!