Thursday, 29 October 2009


Sundogs, also known as parhelia or mock-suns, are optical effects caused by the glint of sunlight hitting millions of ice-crystals within the atmosphere. Ice crystals can be present in high-level cirrus clouds at any time of year, because of the coldness of the atmosphere at that height.

Sundogs are relatively common, but because of their proximity to the sun, they tend to go unnoticed, and often disappear within minutes. Usually they are relatively faint, but occasionally they may be bright. I photographed this sundog late last year, and to my great regret, it was brighter before I took the photographs!

In the middle image there is a faint vertical rainbow-coloured smudge near the power lines that is probably a fragment of a supralateral arc. You can read more about spotting and identifying these fascinating phenomena at Les Cowley's Atmospheric Optics site here.

If you're new to halo-spotting, read this page about the 22-degree halo first. Once you've found the 22-degree halo, finding other haloes becomes easier, and this page also has important information about protecting your eyes.


Anonymous said...

Grace, I love these images, especially the third one. I wonder how it prints?

Grace Dalley said...
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Grace Dalley said...

Thank you, Leigh :-)
Sounds a little like a hint ;-)

Anonymous said...

It is!!!