Saturday, December 04, 2010

Haloed sun

We walked around the northeast corner of the dunes at Boundary Bay, just before sundown. It was a chilly day, and the tide was high again, but the Bay was busy with flocks of Canada geese, gulls, assorted ducks, and sandpipers. Eagles kept watch from dead trees on the dunes. And the late afternoon sky was first dramatic, and finally astounding:

Clouds over the dunes. Looking west, towards the sun.

10 minutes later, looking northwest.

Ice halo, just before sunset.

5 minutes later. As the sun drops behind the hills, the rays stand out more vividly.
 These halos form when sunlight passes through high cirrus clouds containing ice crystals.
Light passing through the hexagonal ice prisms is deflected twice, which produces deviation angles ranging from 22° to 50°. Lesser deviation results in a brighter halo along the inner edge of the circle, while greater deviation contribute to the weaker outer part of the halo. As no light is refracted at smaller angles than 22° the sky is darker inside the halo. (from Wikipedia)
(Diagram from the University of Illinois WW2010 Project.)

The border of the halo is 22° from the sun, here at the horizon. Just at this border, a rainbow effect is visible, with the red on the interior, the blue on the outer edge.

This halo is combined with a ray pattern, and a lower-lying cloud which distorts some of the rays.

Zooming in, to see the textures (faintly) in the lower layer of ice and clouds.
 A Skywatch post


  1. I wonder if the same thing happens with the moon? I've seen something very similar to this on bright, full moon nights.

    These are wonderful was so lucky you were there at just the right time!

  2. Waa, awesome! Never seen that phenomenon before. i really liked..

  3. Ohmygoodness, Susannah - that is one of the most awesome halos I have ever seen! We sometimes get little ones around the sun ... more often around the moon ... but WOW. Never like this! The beauty of your photos brought tears to my eyes.

  4. I adore the way you look at the world; one of my absolute favourite blogs


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