Coronal Rings Above Lac Seul, Ontario

January 08, 2009


Photographer: Rick Stankiewicz
Summary Author: Rick Stankiewicz

The photo above showing stunning coronal rings about the setting Sun was captured over Lac Seul, Ontario, Canada, on June 20, 2008. I had not witnessed this optical effect before. It's likely that the coronal rings were caused by tree pollen in the atmosphere. I suggest this explanation because of the time of year was June, a time in northern Ontario when trees are producing considerable amounts of pollen. Another indication is the oblong shape, which is characteristic of pollen-based coronae. There did not appear to be evidence of a significant pollen release, usually obvious on the surface of local water bodies, nonetheless, pollen sufficient to deflect sunlight (typically greater than 2,000 grains per cubic meter) could have been present in the atmosphere. Coronae are phenomena caused by diffraction of sunlight by minute particles in the air. This summer's eve was further enhanced by thin bands of stratus clouds stretching along the western horizon.

Photo details: Canon 400D camera; 17 to 70 mm Sigma lens; at 100 ISO; f/11, exposure between 1/400 and 1/500 seconds.