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Iridescent clouds have rainbow colors

Iridescent clouds: Dark cloud with cap of rainbow colors on dark sky.
View at EarthSky Community Photos. | Soumyadeep Mukherjee in Kolkata, West Bengal, India, captured this photo of iridescent clouds on August 5, 2021, and wrote: “Iridescent clouds, also known as rainbow clouds, are an optical phenomenon caused by diffraction of sun/moonlight on water droplets or small ice crystals on clouds. This image was captured before sunset. As I woke up after a noon nap and looked through the window, I was greeted by this beautiful cloud and I had to run. I took the wrong lens and the whole thing wouldn’t fit on the frame. Hence, a two-shot handheld panorama. I’m glad that it came out decent.” Thank you, Soumyadeep!

Clouds with rainbow colors

Sky watchers often report seeing rainbow colors in clouds. There are many different kinds of rainbow features you might see associated with clouds, such as halos and colored arcs and even true rainbows. But – if the rainbow-like colors are randomly distributed, and if the sun is nearby in the sky – what you’re seeing is likely an iridescent cloud.

These sorts of clouds are caused by particularly tiny ice crystals or water droplets in the air. Larger ice crystals produce lunar or solar halos, but tiny ice crystals or water droplets cause light to be diffracted – spread out – creating this rainbow-like effect in the clouds.

The images on this page are mostly via the EarthSky community. Our thanks to all who contributed!

By the way, it’s easy to confuse circumhorizon arcs with iridescent clouds. Here’s how to tell the difference.

Read more about iridescent clouds on Les Cowley’s great website Atmospheric Optics

A gallery of images of iridescent clouds

A wispy cloud with rainbow colors and an airplane flying through it.
Ken Christison wrote on November 18, 2018: “We had some beautiful iridescence in the clouds late this afternoon. Seen from northeastern North Carolina.” Thank you, Ken!
2 clouds with rainbow colors on a blue sky.
Kino Obusan caught these iridescent clouds – one on the right and one on the left – on July 15, 2016, from Batangas, Philippines. “It was my first time to see a rare cloud phenomenon like this.” Thank you, Kino!
Our friend Dave Walker in the UK caught another iridescent cloud in 2013. He wrote,
Our friend Dave Walker in the UK caught another iridescent cloud in 2013. He wrote, “There’s been a lot of very high cloud recently, always a cue for me to look out for more atmospheric optics.”
The best way to see an iridescent cloud is to place the sun itself behind some foreground object, a building or mountain, for example.  Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water. EarthSky Facebook friend Duke Marsh captured this image in 2012 in New Albany, Indiana.
The best way to see an iridescent cloud is to place the sun itself behind some foreground object, a building or mountain, for example. Other aids are dark glasses, or observing the sky reflected in a convex mirror or in a pool of water. Duke Marsh captured this image in 2012 in New Albany, Indiana.
Charles Loyd wrote in 2014:
Charles Loyd wrote in 2014: “I was outside and my 9-year-old daughter looked up and asked why there was a rainbow in the clouds … “
The moon with Jupiter and iridescent clouds, Shot in Greece, by Nikolaos Pantazis?
The moon with Jupiter and iridescent clouds, seen over Greece in 2015 by Nikolaus Pantazis.
Cloud iridescence captured by George Quiroga via Wikimedia Commons.
The colors in an iridescent cloud tend to be subtle and are usually pastel, but in some cases they can be vivid. Here is cloud iridescence captured by George Quiroga in Boynton Beach, Florida, in 2012. Image via Wikimedia Commons.

Bottom line: You might someday see an iridescent cloud. These clouds have rainbow-like colors. They’re caused by very tiny ice crystals or water droplets in the air, which cause light to be diffracted (spread out).

Posted 
August 17, 2021
 in 
Earth

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