22 degree Halo and Corona

These images taken 12 minutes apart show how cloud corona sizes can vary but the 22 degree ice halo does not. In the left image the radius of the second corona ring is 8 degrees while on the right it is about 4 degrees. The fast moving low cloud which formed the corona was very thin and allowed the outer ice halo to remain visible. Mars is the 'star' in the halo to the lower right.

This composite shows sections from both images to make comparison of the corona size easier. The first ring in the lower section has a similar radius to the second ring in the upper section

Between the sets of images the droplet size doubled from around 4 microns to around 8 microns. The droplets in each cloud must have been very uniform to allow the second ring in the corona to be seen.

Canon EOS 20D   13th December 2005
Wiltshire, England

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