There are at least 12 kinds of rainbows, a new study reveals, and some skip a color or two.

Since the 1950s, rainbow classification has been based on the size of the raindrops that create them. The bigger the drops, the more vivid the colors.

Another attempt organized them by the height of the sun above the horizon. At about 70 degrees, a rainbow is dominated by blues and greens. Closer to the horizon, there are mostly reds and yellows.

“At sunset or sunrise, the color of the sun and the intensity of the incoming light change dramatically,” Ricard said. When the sun is low in the horizon, rays of light must pass through more of the Earth’s atmosphere. “The red manages to go through,” he explained. “Other wavelengths are completely gone.”

Catch the Rainbows

To capture this rainbow diversity, Ricard and his colleagues gathered hundreds of pictures of rainbows, sorting them into 12 categories based on the visibility of the six colors, the strength of the dark band, and whether any supernumerary bands can be seen. One type lacks a band of green, for instance, another is missing blue and violet, and a third type has only red and blue.

The system is so simple that most anyone could look at a picture of a rainbow, put it in a class, and understand what’s going on, he said. A misty red rainbow, for instance, could only be created near sunrise or sunset with tiny raindrops.

Source: Some Rainbows Don’t Have Every Color of the Rainbow