You can sometimes see bands of rainbow-like colors in the clouds. These are called sundogs. Even though they have colors like rainbows, they are very different. Why?
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With a rainbow, the sunlight is refracted and reflected by the raindrops, letting you see the colors of the spectrum. Because the light is reflected by the raindrops, you need to be facing away from the Sun to see a rainbow.
For a sundog, you have to be facing towards the Sun. The sundog will be about 22° from the Sun, and level with the Sun on one or both sides. Notice the band of color on each side of the Sun in the photo above. Those are sundogs.
Sundogs are caused by high cirrus or cirrostratus clouds made of flat, hexagonal crystals of ice instead of liquid rain. Updrafts in the cloud can cause the ice crystals to align in the same direction, letting them act as prisms to separate the colors of light.
