Optics Galore
A corona, crepuscular rays, cloud shadows and a silver lining. All captured by Alfred Lee at Nai Chung, Hong Kong, China.
©Alfred Lee, shown with permission.


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A sundog or 22° halo fragment at Tsim Sha Tsui, Hong Kong.
The corona is formed by almost uniform sized water droplets. Their source is uncertain. Pileus forming above rising cumulus gives vivid iridescence or corona fragments but its characteristic 'cap' shape is not evident here. Note however the faint iridescence elsewhere on the upper edge of the cumulus.

The sun rays apparently radiating upwards are downward going 3D shadow tubes formed by the thunder cloud. The dark zone around the thunder cloud is, however, its 2D shadow cast onto a lower cloud layer.

Every cloud does not have a silver lining. But most cumulus clouds do when viewed against the light. Where a cloud is thin � as at its edge � sunlight is scattered mostly by one or two encounters with droplets. The light is scattered mostly in the forward direction and forms the �silver� rim. Sunlight penetrating deeper into the cloud is scattered many times and loses its directionality. It is also progressively absorbed and thus clouds viewed contre jour are dark. Nonetheless they do show some light and often with surprising colours.