Photographer's Note

Interesting and huge iridescences above Ponte Tresa
in Italy. In the workshop another more complete shot of the phenomenon.

This is quite a common phenomenon but this occurs close to the sun and to realize that the clouds are showing iridescences you need to mask the sun with the hand, a tree, or anything else.

Sometimes you can see that certain parts of clouds show iridescent colours. In most cases this iridescence appears in clouds which form rapidly (e.g. altocumulus lenticularis). Especially the rims of these clouds have purple red, blue and green colours. This phenomenon is closely related to the coronae. Here the colours are also caused by the diffraction of light. The water droplets that cause the iridescence are very small. Small droplets generate very big coronae with wide rings of the same colour. This is the reason why great parts of the cloud have the same colour. The other colours in the iridescent cloud are less due to the changing distance from the sun, but to different sizes of the droplets. Different droplet sizes generate different coronae, what makes the colour differ despite the equal distance from the sun.

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Additional Photos by mauro locatelli (nilolabrador) Gold Star Critiquer/Silver Workshop Editor/Gold Note Writer [C: 336 W: 15 N: 211] (1469)
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