December Sun Dog

On December 2nd I was returning home from shopping late in the afternoon. It was getting close to dusk, and the dark clouds in the west had already swallowed up the sun. As I turned down one road, heading west, I saw a brilliant rainbow-hued light in the sky: a sun dog. It was so bright I knew I had to photograph it, but needed a good spot with an open view of the sky. I was close to the Eagleson ponds so I figured I might as well stop in there before it disappeared. I pulled up to the entrance on Meadowbreeze Drive, got out, and started shooting.

Sun dogs are very common, but are seldom noticed. They appear twice a week in North America, on average, no matter what time of year it is. They are best seen when the sun is low in the sky, and since the sun rises and sets later in the winter than in the summer, most people tend to see them only in the winter months and associate them with cold weather. Sometimes they are so bright it appears as if there are three suns in the sky; at other times, only a smudge of colour is visible.

Ice crystals in cirrus clouds three to six miles (5 to 10 km) high have a hexagonal molecular structure. The six-sided crystal may be thin, like a sheet of paper (called plates), or thick, like an Allen key (called columns). The angles between the sides of the crystal are constant: the angle between the hexagonal-shaped face and one of the six sides is always 90°, while the angle between two sides is always 120°. Sunlight shining through the crystal is refracted as it changes direction while passing through different faces, sending prisms of light in predictable directions. The type of crystals present (plate or column), and the orientation of the crystals to the sun determine the type of halo that appears in the sky. Most ice crystals within a cloud are aligned in the same direction as a result of air resistance as the crystals slowly drift down. For sun dogs to form, plate crystals must be almost horizontal, while the sunlight enters through one side and leaves through another at a 60° to the first. In comparison, the crystals that create the familiar 22° halo around the sun are columnar.

As it was getting close to dusk, a number of geese were flying in to roost on the ponds for the evening. I thought the geese flying in front of the sun dog as they approached the ponds would make for some spectacular photos, and spent several minutes waiting for flocks to pass directly in front of the rainbow patch of light. Fortunately the sun dog didn’t dissipate – sometimes they appear only briefly as the clouds coalesce and then disperse – and I ended up with quite a few photos that I was pleased with. This one is my favourite; I have it set as my desktop wallpaper.

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I was thrilled to get some interesting photos of wildlife interacting with the sun dog. While I often see sun dogs, sun pillars and 22° halos in the winter months, it’s not often I get the chance to to see birds flying in front of them!

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