Shimmering clouds and good wine

Last week I got an email with a photo showing a cloud that had erupted into a rainbow of color. There is a name for what happened: it’s called cloud iridescence or irisation. Some call it cloud rainbows.

What happens is individual ice crystals or water droplets in the cloud reflect, refract and disperse incoming sunlight. It’s like what happens when a rainbow develops. A rainbow is caused by refle...