Have you ever seen a rainbow that looks like a smile? Most rainbows are shaped like a frown. Rainbows are something called an optic effect. This allows us to see a colorful arc in the sky. Rainbows require two things to happen at the same time: rain and sunlight. Seems strange, right? Sometimes the Sun appears while it is still raining, and we see the sunlight through the raindrops. The raindrops act like tiny prisms. When sunlight enters the prisms, it bends or refracts. When the light is refracted, it breaks apart and creates the seven colors of the rainbow.
Sometimes a rainbow is upside down. The frown shape turns upside down into a smile shape. This is called a circumzenithal arc. Circumzenithal arcs occur when sunlight refracts through ice crystals instead of raindrops. The light enters through the flat top of the three-dimensional crystal and exists through one of the sides. Ice crystals are found in high clouds. These clouds are the white wispy strands we see floating across the sky. Circumzenithal arcs are common, but we do not see them often because they can be hidden behind the clouds.
What Do You Think? What kind of weather conditions would cause an upside down rainbow?
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