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   Subsun

A bright subsun seen looking downwards from 11,000m over Italy, late afternoon 18th July 1995. The halo was intermittently visible over the southern and central parts of the country which was covered by a thin cirrus sheet. The halo elongated and contracted as the tilts of the plate crystal mirrors changed. Reflections from lakes and rivers shine through the cloud. Video- Les Cowley.
  
 
Subsun forming rays

The subsun is the most common subhorizon halo. It is a direct reflection of the sun from millions of cloud crystals acting together as a giant mirror. Plate crystals are the usual source. Rays can reflect externally off the uppermost horizontal face or internally from the lowermost.

The halo can be an almost circular image of the sun but it becomes elongated the more the crystals wobble and tilt until eventually a lower sun pillar results. We usually see something between these two extremes.