What's the 'rainbow' cloud I saw today...it wasn't raining...how could that be?
Many viewers saw what appeared to be a horizontal rainbow-colored 'stripe' across the sky during the noon hour. That 'stripe' isn't a rainbow (it doesn't form with raindrops or even cloud drops), but is actually an arc...a special type of arc called a 'circumhorizon arc'. Not a term that exactly rolls off the tongue. It's found when the sun is high in the sky and ice crystals are present in high, thin cirrus clouds. The sunlight splits or 'refracts' into it's component colors, reflecting off the interior 'faces' of the ice crystals. When the angle between the sun and the falling ice crystals is just right, the 'arc' we saw today will develop.