You don't need rain for these rainbows spotted over Ottawa

If you happened to look up at the sky this past weekend, you might have noticed a rare and beautiful sight: iridescent rainbow clouds, but not a drop of rain in sight.

This phenomenon is known, fittingly, as cloud iridescence or irisation. The effect is not unlike seeing a rainbow painted on the clouds. The term comes from Iris, the Greek personification of the rainbow.

Some of our CBC audience members managed to capture images of the event, witnessed Saturday and Sunday across the region. 

This type of phenomenon occurs most often in altocumulus, cirrocumulus and especially lenticular clouds, and usually when those clouds are close to the sun or moon in the sky.

Like a rainbow, this beautiful effect is produced when there are suspended water droplets present. But these water or ice droplets are extremely tiny and spread out over a particular type of cloud. The clouds must be thin to allow the light to penetrate and scatter.

The bands and colours change as the cloud evolves.

Iridescence is seen mostly when part of a cloud is forming because then all the droplets have a similar genesis, and consequently a similar size.