Dogging the Sun

A pair of tiny rainbow-like splashes of color sometimes flanks the rising or setting Sun like dogs attending their master. Perhaps that’s why these displays are known as sun dogs.

Regardless of the name, sun dogs faithfully maintain the same distance from the Sun: roughly 22 degrees — twice the width of your fist held at arm’s length. They’re sometimes accompanied by fainter halos that completely encircle the Sun.

Both sun dogs and halos are created by flat ice crystals with six sides. They’re found in thin clouds that pass between the Sun and the viewer. The crystals act as tiny prisms, bending the sunlight. Different colors are bent at different angles, so red appears on the inside, closest to the Sun, and blue on the outside, farthest from the Sun.

The ice crystals that form a halo line up in random directions. As a result, a halo usually is faint and white, with little or no color.

The crystals that form a sun dog, on the other hand, flutter through the clouds like leaves falling from a tree. That makes most of them line up parallel to the horizon. That provides more prisms to bend and split the light, producing brighter and more colorful displays.

Larger crystals wobble more as they descend. That spreads their light across a wider area, producing a larger splotch of color “dogging” the Sun.
 

Script by Damond Benningfield

Today's program was made possible by Mercer Caverns, in Calaveras County in California's historic Gold Country.