Although they look similar to rainbows in their colour arrangement; the mechanism by way the light is scattered to produce them is different.
Rainbows are the result of refraction and reflection. When light is refracted, it is bent by passing through mediums of different densities, such as water. Reflected light bounces off a surface at an angle equal to the angle it hit the surface at. Diffraction, however, involves light waves being scattered into a pattern; creating what you see here.
The clouds needed for these rare events have to be cirrus and at least 20,000 feet in the air, with just the right amount of ice crystals. The sun also has to hit the clouds at precisely 58 degrees.
Photo courtesy of Raymond Lam