Nacreous clouds/ Rainbow clouds.

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These are fire rainbows/rainbow clouds - the rarest of all naturally occurring atmospheric phenomena.The clouds needed for these rare events have to be cirrus and at least 20,000 feet in the air, with just the right amount of ice crystals.The sun also has to hit the clouds at precisely 58 degrees.

These clouds are caused by light passing through wispy, high-altitude cirrus clouds and the ice crystals must be shaped like thick plates with their faces parallel to the ground.When light enters through a vertical side face of such an ice crystal and leaves from the bottom face, it refracts, or bends, in the same way that light passes through a prism. If a cirrus's crystals are aligned just right, the whole cloud lights up in a spectrum of colours just like it did today for me on the way home!The phenomenon is quite rare because the ice crystals must be aligned horizontally to refract the high sun.these another thing to note in these spectacular events is that they can be very short-lived, rarely surviving beyond half an hour, simply because all of the factors involved must be just so before it can happen. Just look up.