Cloud Iridescence

Remember the phrase "Roy G. Biv" which is a way to memorize the colors of the rainbow from red to violet. This will give you the colors of the rainbow in the correct order. You need to know that some researchers do not include the indigo color as this indicates a color too vague to tell the difference between it and blue. When you look at a rainbow, the red color will be on top and the violet color will be on the inner aspect of the arch. In general, the inside of a rainbow is brighter than the outside.

If by some chance light is reflected twice inside a raindrop, you will see a double rainbow. This is a secondary and more faint rainbow above a brighter one. You might notice that this rainbow is reversed. The secondary rainbow will be red on the inside and violet on the outside. It is possible to have more than 2 rainbows, although they are harder to see because of their faintness.

There are several rare rainbows you can see. A red rainbow is seen at sunrise or sunset. You only see reddish colors because the blue and violet colors and become scattered by the thicker atmosphere. The fogbow can be seen when the droplets inside fog reflect and refract light in the same way you see in clouds. Some will have reddish colors and bluish colors only, while others may be white, mostly because these are very small droplets of water. A moonbow or lunar rainbow happens because of light that has become reflected off the moon first.

CLOUD IRIDESCENCE

Cloud iridescence is very colorful and is an optical illusion you might see whenever a cloud is near the sun or the moon. They often look iridescent, similar to how you see soap bubbles on a watery surface. It is most commonly seen near altocumulus, cirrus, or cirrocumulus clouds. The reason you see this is because of the refraction of light from the ice crystals or water droplets in the cloud. You need to have fairly small and uniform crystals in order to see this phenomenon. It is best seen at the very edges of a cloud.