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What causes rainbow colors in clouds?

Iridescent clouds – clouds with rainbow colors – happen when especially tiny water droplets or small ice crystals individually scatter light.

Kino Obusan caught this iridescent cloud on July 15, 2016 from Batangas, Philippines.

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!

Sky watchers sometimes report seeing rainbow colors within clouds. These colorful clouds are called iridescent clouds. When you see a cloud like this, you know there are especially tiny ice crystals or water droplets in the air. Larger ice crystals produce solar or lunar halos, but tiny ice crystals or water droplets cause light to be diffracted – spread out – creating this rainbow-like effect in the clouds.

The phenomenon is called cloud iridescence or irisation. The term comes from Iris, the Greek personification of the rainbow.

The images on this page are mostly via EarthSky friends on Facebook and Google+. Our thanks to all who contribute!

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

Laura Berry caught these iridescent clouds on May 31, 2016. Thanks, Laura!

Laura Berry caught these iridescent clouds on May 31, 2016. Thanks, Laura!

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. EarthSky Facebook friend Duke Marsh captured this image in 2012 in New Albany, Indiana.

Karthik Easvur in Pondicherry, India wrote in November, 2015:

Karthik Easvur in Pondicherry, India wrote in November, 2015: “I was just seeing the sun being covered by a layer of grey clouds … and for the first time saw something like this … “

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 … “

Iridescent clouds seen by EarthSky Facebook friend Mike O'Neal in Oklahoma on May 27, 2013.  Thank you, Mike.

Iridescent clouds seen by EarthSky Facebook friend Mike O’Neal in Oklahoma in 2013. Thank you, Mike.

Iridescent Kelvin-Helmholtz clouds with passing swallow, Mutare, Zimbabwe Photo taken March 11, 2016 by Peter Lowenstein.

Iridescent Kelvin-Helmholtz clouds with passing swallow, Mutare, Zimbabwe Photo taken March 11, 2016 by Peter Lowenstein.

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 on occasion see a rainbow-like cloud. They are fairly rare, but people do spot them, and we sometimes receive photos of them. They’re caused by the presence of very tiny ice crystals or water droplets in the air, which cause light to be diffracted or spread out.

Deborah Byrd

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