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 beautifulsight: iridescent rainbow clouds, butnot a drop of rain in sight.

This phenomenon is known, fittingly, ascloud iridescenceoririsation. 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 phenomenonoccurs 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 wateror ice droplets are extremelytiny and spread out over a particular type of cloud. The clouds must be thin to allow the light to penetrate andscatter.

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.